La postmodernité, modifiant les repères essentiels de l'humanité que sont la durée, l'espace, la constitution du sujet, le statut de la mort et de l'absence, a affecté en profondeur le contexte dans lequel s'élabore le concept de sacré. Il en résulte une forme moderne de sacré dévoyé procédant davantage d'une mythologie résiduelle, d'une initiation tronquée ou, selon les mots de Mircea Eliade, de ritualismes dégradés, que d'un sacré systémique ayant une portée décisive, notamment, dans la détermination des valeurs et l'élaboration d'un destin commun. Or, la crise de l'éducation serait entée sur le déclin du sacré,départi de sa dimension structurelle. Le sujet contemporain, qui se cherche entre jouissance immédiate et relativisme désenchanté, ne semble plus pouvoir compter sur le potentiel fédérateur d'une éducation fragilisée, et l'altération de celle-ci paraît inéluctable, à moins que, nous engageant dans un autre temps nous n'admettions l'évidence de notre attachement phénoménologique et que nous ne sachions, en la préservant dans le langage, accepter la négativité du monde. / Postmodernity, modifying humanity's reference points - duration, space, subject's formation, status of death and non-attendance -, deeply affects the context in which the concept of sacred usually develops. The outcome is a kind of modern sacred, proceeding from a residual mythology, a rigged initiation or, in the own words of Mircea Eliade, from degraded ritualisms, and not a systemic sacred that would have any decisive impact on values determination or would draw up any common destiny.The education crisis would be a consequence of the declining sacred, deprived of its structural dimension. The contemporary subject, who is wavering between instantaneous enjoyment and disenchanted relativism, can't trust anymore the federating power of a weaken education, unless we admit the obvious of our phenomenologic statement and we are able to agree, preserving it inside the language, the negativity of the world.

Le complexe SAGA (Spt-Ada-Gcn5 acetyl transferase) est un co-activateur transcriptionel, conservé chez les eucaryotes, qui participent à la transcription d’environ 10% des gènes chez la levure, où il fait le lien entre les composants du complexe de pré-initiation, tel que la TATA-box Binding Protein (TBP) et des activateurs, et modifie les histones dans le contexte de la chromatine (acétylation et déubiquitination). Ces travaux de thèse ont permis de décrire l’architecture moléculaire du complexe observée par microscopie électronique. Nous avons pu (i) localiser le module de déubiquitination au sein du complexe entier et ainsi (ii) définir une zone d’interaction avec le nucléosome ; (iii) montrer la présence de deux sites d’interaction avec la protéine TBP situé au niveau d’une « pince »moléculaire ; (iv) observer un lien fonctionnel entre le module de déubiquitination, en particulier de la protéine Sgf73, et les conformations adoptées par cette pince. / The SAGA complex (Spt-Ada-Gcn5 acetyl transferase) is a transcriptional coactivator, highly conserved in eukaryotes, involved in the transcription of 10% of the genes in yeast, where it bridges the components of the pre-initiation complex such as the TATA-box Binding Protein (TBP) and activators, as well as modifies histones in the chromatin template (acetylation and deubiquitination). This work has revealed the molecular architecture of the complex observed by electron microscopy. We could (i) localize the deubiquitination module within the whole complex and thus (ii) define the interaction surface with the nucleosome; (iii) reveal the presence of two TBP-interacting surfaces localized at the tips of a molecular clamp; (iv) observe a functional link between the deubiquitination module, in particular the Sgf73 protein, and the conformation adopted by this clamp.

Le spiritisme apparaît comme un mouvement religieux populaire qui emphatise les charismes aux États-Unis autour de 1848. Traversant l’Atlantique, il revêt la forme d’une doctrine aux influences progressistes et anti-cléricales sous la plume d’Allan Kardec, son « codificateur » français, qui lui donne son patronyme en 1858. Enfin, il connaît une « religiosification » au Brésil dans les décennies qui suivent. Le kardécisme moderne est aujourd’hui considéré comme l’une des religions les plus importantes de ce pays, et compte des adeptes partout dans le monde. Ce travail s’intéresse d’abord à la pratique kardéciste contemporaine sur les trois continents historiques de son élaboration. L’ethnographie comparée des centres visités dans la Bay Area de San Francisco (États-Unis), à Paris (France) et à Salvador de Bahia (Brésil) montre une stabilisation du kardécisme autour de références communes. Les profils des « convertis », les modi operandi, les caractéristiques et le statut du savoir au sein des groupes sont autant d’éléments qui pointent la constitution d’une identité spirite transnationale uniformisée en dépit d’adaptations marginales des pratiques localement. Dans un second temps, le kardécisme retiendra notre attention en tant qu’avatar initiatique. Le travail sur soi, moral et expérimental, qu’exigent l’apprentissage médiumnique et la réforme intime, les deux piliers de la doctrine, est vecteur d’une transformation ontologique – pivot de la logique initiatique. En effet, l’initiation promeut un « changement de statut » chez l’aspirant à l’initiation. Mais l’initiation consiste aussi à instiller un sens du sacré. Là encore, l’interaction médiumnique est le siège d’un certain mystère. Si ces caractéristiques de l’initiation semblent préservées dans le kardécisme moderne, c’est sous une forme diluée, rationalisée – dès lors, le kardécisme ne témoigne-t-il pas des déplacements du sacré? / Spiritualism appeared in the USA around 1848 as a popular religious movement which emphasized charisma. Crossing the Atlantic Ocean it took on the form of a doctrine influenced by progressivism and anticlericalism as instigated by Allan Kardec, its French “codifier” who named it in 1848. Finally it underwent a “religiosification” in Brazil in the following decades. Nowadays modern Kardecism is considered to be one of the prevailing religions in Brazil and has followers all over the world. This research aims, first, to deal with contemporary Kardecist observance on the three historical continents of its elaboration. The comparative ethnography of the centers visited in San Francisco’s Bay Area (USA), in Paris (France) and in Salvador (Bahia, Brazil) reveals a stabilization of Kardecism around common references. The profiles of the “converts”, the procedures, and the characteristics and status of knowledge within the groups are all elements that point to the formation of a transnational Kardecist identity standardized despite minor variations in local practices. Secondly, we will focus on Kardecism as an initiatic manifestation. Concern for the self, both moral and experimental, required by the learning of mediumship and the “personal reform” which are the two pillars of the doctrine, is central to an ontological transformation, the mainspring of the initiatic process. Indeed initiation promotes a “change of status” in the personhood of the candidate for initiation. But initiation also involves awakening a sense of the Sacred in the candidate. However, the mediumnic interaction – i.e. the relationship between the medium and his/her spirits – remains somehow mysterious. These mentioned characteristics of initiation do seem preserved in modern Kardecism but in a diluted, rationalized form. Can then Kardecism help recognize the evolutions of the Sacred ? / O Espiritismo aparece como um movimento religioso popular que enfatiza os carismas nos Estados Unidos por volta de 1848. Cruzando o Atlântico, assume a forma de uma doutrina de influências progressistas e anti-clericais nos escritos de Allan Kardec, seu "codificador" francês, que lhe dá seu nome em 1858. Finalmente, experimenta uma "religiosificação" no Brasil nas décadas que se seguem. O kardecismo moderno é hoje considerado uma das religiões mais importantes deste país, e conta com seguidores em todo o mundo. Este trabalho se interessa principalmente com a prática kardecista contemporânea nos três continentes históricos do seu desenvolvimento. A etnografia comparativa dos centros visitados na área da baía de São Francisco (EUA), Paris (França) e Salvador da Bahia (Brasil) mostra uma estabilização do kardecismo em torno de referências comuns. O perfil dos "convertidos", os modi operandi, as características e status de conhecimento dentro do grupo são elementos que apontam a constituição de uma identidade espírita transnacional padronizada, apesar das adaptações marginais de práticas locais. Em segundo lugar, o kardecismo retêm nossa atenção como um avatar iniciático. O trabalho sob si mesmo, moral e experimental, exigido pelo ensino mediúnico e pela reforma íntima, os dois pilares da doutrina, é vetor de uma transformação ontológica – pivô da lógica iniciática. Na verdade, a iniciação promove uma "mudança de status" no aspirante à iniciação. Mas a iniciação consiste também em incutir um sentido do sagrado. Mais uma vez, a interação mediúnica é a sede de um certo mistério. Essas características de iniciação parecem preservadas no kardecismo moderno de uma forma diluída, racionalizada – mostraria, portanto, o kardecismo a circulação do Sagrado ?

<p>Ribosomes are the universal ribonucleoprotein organelles that translate the genetic message from mRNA to protein. In prokaryotes, the ribosomal subunits are 30S and 50S subunit, which bind together during the translation process forming 70S ribosome. The ribosome is a highly dynamic structure, and acts as a working platform for the different factors involved in the process of converting the genetic information into protein.</p><p>Cryo-electron tomography (cryo-ET) is an emerging imaging technology that combines the potential of three-dimensional (3D) reconstruction at molecular resolution with a close-to-native preservation of the specimen. Here, we have applied this method to reconstruct rifampicin-treated <i>Escherichia coli</i> individual 30S subunits in vitro and in situ, and individual 50S subunits in situ. In the 30S subunit, the head, the platform and the body show large conformational movements relative to each other. The particles are grouped into three conformational groups according to the width/height ratios. Also, an S15 fusion protein derivative has been used as a physical reporter to localize S15 in the 30S subunit. In the 50S subunit, the L1 stalk, the L7/L12 stalk, the central protuberance (CP), and the peptidyl transferase center (PTC) cleft are the most dynamic and flexible parts in the reconstructed structures with clear movements indicated. Different locations of the tunnel in the central cross-sections through the in situ 50S subunits indicate a flexible pathway inside the large subunit. In addition, gross morphological changes were also been observed in our reconstructions. Our results demonstrate a considerable conformational flexibility among individual ribosomal subunits, both in vitro and in situ.</p><p>Translation is an essential process for all cells and organisms. Translation initiation is the rate-limiting step and the most highly regulated phase of translation process. Several regions along the mRNA have been reported to influence translation initiation. The Shine-Dalgarno (SD) sequence located 5-9 bases upstream of the initiation codon supports translation initiation by complementary binding to the Anti-Shine-Dalgarno (ASD) sequence on the 16S rRNA.</p><p>We have here compared how an SD⁺ sequence influences gene expression, if located upstream or downstream of an initiation codon. The positive effect of an upstream SD⁺ is confirmed. A downstream SD⁺ gives decreased gene expression. If an SD⁺ is placed between two potential initiation codons, initiation takes place predominantly at the second start site. The first start site is activated if the distance between this site and the downstream SD⁺ is enlarged and/or if the second start site is weakened. Upstream initiation is eliminated if a stable stem-loop structure is placed between this SD⁺ and the upstream start site. The results suggest that the two start sites compete for ribosomes that bind to an SD⁺ located between them. A minor positive contribution to upstream initiation resulting from 3’ to 5’ ribosomal diffusion along the mRNA is suggested. Since the location of SD⁺or SD-like sequences can strongly influence gene expression, this should be of significant evolutionary importance.</p>

Ribosomes are the universal ribonucleoprotein organelles that translate the genetic message from mRNA to protein. In prokaryotes, the ribosomal subunits are 30S and 50S subunit, which bind together during the translation process forming 70S ribosome. The ribosome is a highly dynamic structure, and acts as a working platform for the different factors involved in the process of converting the genetic information into protein. Cryo-electron tomography (cryo-ET) is an emerging imaging technology that combines the potential of three-dimensional (3D) reconstruction at molecular resolution with a close-to-native preservation of the specimen. Here, we have applied this method to reconstruct rifampicin-treated Escherichia coli individual 30S subunits in vitro and in situ, and individual 50S subunits in situ. In the 30S subunit, the head, the platform and the body show large conformational movements relative to each other. The particles are grouped into three conformational groups according to the width/height ratios. Also, an S15 fusion protein derivative has been used as a physical reporter to localize S15 in the 30S subunit. In the 50S subunit, the L1 stalk, the L7/L12 stalk, the central protuberance (CP), and the peptidyl transferase center (PTC) cleft are the most dynamic and flexible parts in the reconstructed structures with clear movements indicated. Different locations of the tunnel in the central cross-sections through the in situ 50S subunits indicate a flexible pathway inside the large subunit. In addition, gross morphological changes were also been observed in our reconstructions. Our results demonstrate a considerable conformational flexibility among individual ribosomal subunits, both in vitro and in situ. Translation is an essential process for all cells and organisms. Translation initiation is the rate-limiting step and the most highly regulated phase of translation process. Several regions along the mRNA have been reported to influence translation initiation. The Shine-Dalgarno (SD) sequence located 5-9 bases upstream of the initiation codon supports translation initiation by complementary binding to the Anti-Shine-Dalgarno (ASD) sequence on the 16S rRNA. We have here compared how an SD+ sequence influences gene expression, if located upstream or downstream of an initiation codon. The positive effect of an upstream SD+ is confirmed. A downstream SD+ gives decreased gene expression. If an SD+ is placed between two potential initiation codons, initiation takes place predominantly at the second start site. The first start site is activated if the distance between this site and the downstream SD+ is enlarged and/or if the second start site is weakened. Upstream initiation is eliminated if a stable stem-loop structure is placed between this SD+ and the upstream start site. The results suggest that the two start sites compete for ribosomes that bind to an SD+ located between them. A minor positive contribution to upstream initiation resulting from 3’ to 5’ ribosomal diffusion along the mRNA is suggested. Since the location of SD+ or SD-like sequences can strongly influence gene expression, this should be of significant evolutionary importance.

The studies reported in this thesis address firstly, the biology of a modified nucleoside, Queuosine (Q) and secondly, the properties of mitochondrial translation initiation factor 2. A summary of the relevant literature on both these topics is presented in Chapter 1. Section I of this ‘General Introduction’ summarizes the literature on biosynthesis and physiological importance of Queuosine. Section II is a brief review of the current understanding of translation initiation in Eubacteria. Information about the mitochondrial translation initiation apparatus also features as a subsection. The next chapter (Chapter 2), describes the ‘Materials and Methods’ used throughout the experimental work presented in the thesis. It is followed by three chapters containing experimental work as described below:- i) Biosynthesis of Queuosine (Q) in Escherichia coli Q is a hypermodification of guanosine found at the wobble position of tRNAs with GUN anticodons. Q is thought to be produced via a complex multistep pathway, the details of which are not known. It was found in our laboratory that a naturally occurring strain of E. coli B105 lacked Q modification in the tRNAs. As the known enzymes of Q biosynthesis were functional in this strain, it presented us with the opportunity to uncover novel component(s) of Q biosynthetic pathway. In the present work, a genetic screen was developed to map the defect in E. coli B105 to a previously uncharacterised gene, ybaX, predicted to code for a 231 amino acid long protein with a pI of 5.6. Further genetic analyses showed that YbaX functions at a step leading to production of preQ0, the first known intermediate in the generally accepted pathway that utilizes GTP as the starting molecule. The gene ybaX has been renamed as queC. Using a combination of bioinformatics based prediction and gene knockouts, we have also been able to place two more genes, queD and queE at the initial step in Q biosynthesis, suggesting that the initial reaction of Q biosynthesis might be more complex and mechanistically different than what has been proposed earlier. ii) Caenorhabditis elegans as a Model System to Study Queuosine Metabolism in Metazoa Animals are thought to obtain Q (or its analogs) as a micronutrient from dietary sources such as gut microflora, and the corresponding base is then inserted in the substrate tRNAs by tRNA guanine transglycosylase (TGT). In animal cells, changes in the abundance of Q have been shown to correlate with diverse phenomena including stress tolerance, cell proliferation and tumor growth but the precise function of Q in animal tRNAs remains unknown. A major obstacle in the study of Q metabolism in higher organisms has been the requirement of a chemically defined medium to cause Q depletion in animals. Having discovered that E. coli B105 has a block in the initial step of Q biosynthesis, we reasoned that this strain could be used as a Q- diet for organisms like C. elegans, which naturally feed on bacteria. An analysis of C. elegans tRNA revealed that as in the other higher animals, tRNAs in the worm C. elegans, are modified by Q and its sugar derivatives. When the worms were fed on Q deficient E. coli B105, Q modification was absent from the worm tRNAs suggesting that C. elegans lacks a de novo pathway of Q biosynthesis. The inherent advantages of C. elegans as a model organism, the speed and simplicity of conferring a Q deficient phenotype on it, make it an ideal system to investigate the function of Q modification in tRNA. By microinjecting tgt-1-gfp constructs into C. elegans, we could also demonstrate that a major form of TGT is localised to the nucleus, suggesting that insertion of Q into the tRNAs could be occurring in the nucleus. iii) Dual Function of Bovine Mitochondrial Initiation Factor 2 as Initiation Factors 1 and 2 in Escherichia coli Translation initiation factors 1 and 2 (IF1 and IF2) are known as ‘universal translation initiation factors’ due to the presence of their homologs in all living organisms. Homologs of these factors are also present in the chloroplast, however, a unique situation exists in the mitochondria where IF2 homolog (IF2mt) is known to occur but an IF1 like factor is not found. We have engineered a system of E. coli knockouts to allow the study of IF2mt in a prokaryotic milieu. We found that the bovine IF2mt complements an E. coli strain wherein the gene for IF2 is knocked out, providing the first proof of a mitochondrial translation initiation factor working in a eubacterial system. This conservation of function is especially interesting in light of the recent reports revealing significant differences between the mitochondrial and eubacterial ribosomes. Further, we found that the IF2mt can also support a double knockout of IF1 and IF2 genes in E. coli, suggesting that IF2mt possesses both IF1 and IF2 like activities in E. coli. This finding offers an explanation for the lack of an IF1 like factor in mitochondria. Molecular modeling of bovine IF2mt indicated that a conserved insertion found in all mitochondrial IF2s, may form a protruding α-helix that could stabilize IF2mt on ribosomes. This insertion could in principle function as IF1 and we have explored the role of this conserved insertion both in vivo and in vitro, by generating mutants of IF2mt and EcoIF2, to lose or gain the conserved insertion respectively.

<p>RÉSUMÉ</p><p>Au Sénégal, on estime que 28% des femmes sont victimes de MSF et les Diolas sont une des ethnies au Sénégal qui pratique cette tradition. Dans ce mémoire, j’ai l’intention en premier de comprendre et d’interpréter les raisons qui justifient, selon les Diolas, cette pratique par la méthode d’abduction et selon la théorie du néo-institutionnalisme. Mon intention en second lieu est de comprendre les éléments de la prétendue diminution de cette pratique dans certaines zones chez les Diolas. Je veux aussi comprendre le rôle de l’ONG Tostan dans la réduction de ce phénomène. Pour réaliser mon projet d’étude, j’ai fait mon étude de terrain dans deux villages au sud du Sénégal.</p><p>Le résultat que j’ai obtenu est que les Diolas prennent les MSF comme étant la première phase, c'est-à-dire la première partie du cycle d’initiation d’une femme. Une fille ne peut pas entrer dans la deuxième partie de son cycle d’initiation qui est une partie essentielle pour réussir dans la société Diolas si elle ne passe pas la première partie grâce aux MSF. En plus, j’ai compris que les raisons principales pour justifier cette pratique sont que les Diolas pensent que c’est une recommandation islamique. Donc, la pratique des MSF est venue avec l’islamisation.</p><p>Après les programmes habituels de Tostan dans les villages, les deux villages de mon étude de cas ont fait leur déclaration publique contre les MSF. Selon les villageoises, dans le premier village, le rôle de Tostan est qu’elle les avait aidées à sensibiliser et à stabiliser le village dans l’abandon de la pratique. Mais il faut souligner que le procès d’abandon avait déjà commencé avant l’arrivée de Tostan. Je trouve qu’il y avait des éléments nécessaires pour cesser la pratique qui a existé dans le village avant l’arrivée de Tostan qui a facilité le choix de vraiment laisser la pratique.</p><p>Le deuxième village témoigne de l’importance de Tostan et affirme que sans Tostan, le village n’aurait pas abandonné la pratique des MSF. En même temps, il y a des indicateurs qui montrent que tous les habitants du village n’ont pas cessé la pratique.</p><p>Une remarque inattendue est que la norme féminine est sous transformation. Aujourd’hui, les femmes non excisées sont mieux considérées que les femmes excisées par toute la société dans les villages de cas de cette étude. Une autre observation intéressante est que les villageoises témoignent que les jeunes femmes étaient les plus difficiles à convaincre d’abandonner la MSF contrairement aux femmes plus âgées alors que se sont elles, qui peuvent fondamentalement réclamer d’avoir été préjudiciées a cause de nous au Nord, il est normalement difficile de moduler les différentes traditions à cause des anciennes générations au sein de la société.</p> / <p>An estimated 28% of Senegalese women are victims to Female Genital Mutilation (FGM). The Jola tribe in Senegal is one of the ethnics that practice this tradition. In this thesis, I have the intention to interpret and try to understand the reasons the Jolas have to justify this practice. This will be made by an abdication method with the help of the New Institutional Theory. My purpose is furthermore to understand why the practice of FGM has reduced in some Jola-zones. Furthermore, I would like to comprehend the role of the NGO Tostan in the reduction process. To fulfil my intentions, I have made a Minor Field Study of two case studies conducted in two villages in the south of Senegal.</p><p>The result of this thesis is that the Jolas use FGM as the first phase of the women’s initiation cycle. A girl is not allowed to enter the second phase of her initiation cycle, which is an essential step in order to succeed in the Jolas society, if she has not already passed the first phase. I have understood that the main reason to justify the practice is that the Jolas think that FGM is an Islamic decree. This signifies that the practice of FGM has come to the Jolas with the Islamization.</p><p>After conducting ordinary programs of Tostan in the villages, both case villages have made an official declaration against FGM. According to the villagers in the first village, the role of Tostan was to help them be aware and stabilise so that they could implement the declaration. It is important to stress that the process of abandoning the practice had already started before the intervention of Tostan in this village. This study shows that there already existed certain important elements in the village that had facilitated the work of Tostan.</p><p>The second village confirmed the importance of Tostan and affirmed that they would not have abandoned the practice without the intervention of Tostan. On the other hand, I found indications which show that all the habitants of the village have not yet abandoned the practice.</p><p>One unexpected observation that I achieved to track during my fieldwork is that the female norm is under transformation. Today, the non-circumcised women are considered more attractive than circumcised women. Another interesting observation is that the villagers claimed that it is actually more complicated to convince the younger female generations to abandon the practice of FGM, and not the elder females, which basically can be claimed to be the prejudice we carry with us from the North, when talking about different traditions which are difficult to change because of the old generations in a society.</p>

Le virus de l’immunodéficience humaine de type 1 (VIH-1) est responsable de la pandémie du SIDA (syndrome de l’immunodéficience acquise). Des souches virales résistantes aux antirétroviraux actuellement utilisés apparaissent rapidement. Il est donc important d’identifier de nouvelles cibles dans le cycle de réplication du VIH-1 pour développer de nouveaux agents contre ce virus. La traduction des protéines de structure et des enzymes du VIH-1 est une étape essentielle du cycle de réplication virale. Ces protéines sont exprimées à partir de l’ARN messager (ARNm) pleine-longueur (ARNmPL) à la fin du cycle de réplication. L’ARNmPL du VIH-1 peut utiliser un mode d’initiation de la traduction coiffe-dépendant, comme la majorité des ARNm cellulaires, mais peut aussi utiliser un mode d’initiation alternatif, car sa région 5’ non-traduite (5’UTR) contient un site interne d’entrée du ribosome (IRES), ce qui lui permet d’initier la traduction suivant un mode IRES-dépendant. L’initiation IRES-dépendante permet à l’ARNmPL d’être traduit quand l’initiation coiffe-dépendante est inhibée. L’activité de l’IRES de la région 5’UTR de l’ARNmPL du VIH-1 (IRES5’UTR) est faible dans des conditions physiologiques, mais est stimulée lorsque la cellule est arrêtée à la transition G2/M du cycle cellulaire, un arrêt qu’induit l’infection par le VIH-1. Une grande portion de l’IRES5’UTR, que nous nommons IRES5’UTRc, est présente dans tous les ARNm viraux et a une activité semblable à celle de l’ IRES5’UTR, ce qui indique que le mode IRES-dépendant peut être utilisé par tous les messagers du VIH-1. Lors de mes études doctorales, j’ai caractérisé le fonctionnement de l’IRES5’UTR du VIH-1. J’ai transfecté des cellules lymphocytaires Jurkat T, dérivées des cibles naturelles du VIH-1, avec un vecteur dual-luciférase contenant les séquences codantes des luciférases de la Renilla (Rluc) et de la luciole (Fluc) séparées par la région 5’UTR de l’ARNmPL du VIH-1. La traduction de la Rluc est coiffe-dépendante alors que celle de la Fluc dépend de l’IRES5’UTR. J’ai d’abord effectué une analyse mutationnelle et j’ai identifié trois régions qui stimulent l’activité de l’IRES5’UTR et une tige-boucle qui réprime l’activité de cet IRES, que j’ai nommée IRENE (IRES negative element). J’ai montré que l’effet répresseur d’IRENE est aboli lorsque les cellules sont soumises à un stress oxydatif, un type de stress induit lors d’une infection par le VIH-1. Nous proposons que IRENE maintiendrait l’IRES5’UTR dans une conformation peu active dans des conditions physiologiques. On sait que les IRES sont activés par divers facteurs cellulaires, appelés ITAF (IRES trans-acting factors). Nous proposons que l’IRES5’UTR adopterait une conformation active suite à la liaison d’un ITAF exprimé ou relocalisé lors d’un stress oxydatif. Ces travaux ont fait l’objet d’une publication (Gendron et al., 2011, Nucleic Acids Research, 39, 902-912). J’ai ensuite étudié l’effet de la protéine virale Tat sur l’activité de l’IRES5’UTR. En plus de son rôle essentiel dans la transactivation de la transcription des ARNm viraux, Tat stimule leur traduction coiffe-dépendante, en empêchant l’inhibition d’un facteur d’initiation canonique, eIF2, induite par la protéine kinase modulée par l’ARN double-brin (PKR) et en déroulant la structure TAR présente à l’extrémité 5’ de tous les ARNm du VIH-1. Elle affecte aussi l’expression de plusieurs gènes cellulaires. J’ai montré que les isoformes Tat86 et Tat72, mais non Tat101, stimulent l’activité de l’IRES5’UTR. Cet effet est indépendant de PKR et de TAR, mais dépendrait de la conformation de Tat. Nous proposons que Tat activerait un facteur de transcription cellulaire qui déclenche l’expression d’un ITAF de l’IRES5’UTR ou encore qu’elle activerait directement un tel ITAF. J’ai de plus montré que PKR stimule l’activité de l’IRES5’UTR, ce qui est surprenant puisque PKR est une protéine antivirale. Cet effet est indépendant de l’inhibition d’eIF2 par PKR et pourrait résulter de l’activation d’un ITAF. Sachant qu’une portion active de l’IRES5’UTR, IRES5’UTRc, est présente dans tous les ARNm viraux, notre hypothèse est que la stimulation de cet IRES par PKR permettait de traduire l’ARNm de Tat au début du cycle de réplication, ce qui permettrait ensuite la traduction coiffe-dépendante des ARNm du VIH-1, qui est stimulée par Tat. Ces travaux font l’objet d’un manuscrit (Gendron et al., soumis à RNA). Mes résultats, couplés aux données de la littérature, me conduisent à la conclusion que, à la fin du cycle de réplication du VIH-1, l’activité de l’IRES5’UTR est stimulée par le stress oxydatif, l’arrêt en G2/M et la présence de quantités élevées de Tat, alors que la traduction coiffe-dépendante est compromise. L’initiation IRES-dépendante serait alors indispensable pour que le VIH-1 traduise l’ARNmPL. L’IRES5’UTR constituerait donc une cible très intéressante pour développer des agents anti-VIH. / The human immunodeficiency virus type 1 (HIV-1) is the causative agent of AIDS (acquired immunodeficiency syndrome). Viral strains that are resistant to antiretroviral agents used for the treatment of HIV-1 infected patients rapidly emerge. It is thus important to study the viral replication cycle in order to discover new targets for the development of novel agents against HIV-1. Translation of structural proteins and viral enzymes is a key step of the viral replication cycle. These proteins are translated from the HIV-1 full-length mRNA during late stages of the replication. This mRNA can be translated by a cap-dependent mode which is used by the majority of cellular mRNAs. However, since its 5’ untranslated region (5’UTR) contains an internal ribosome entry site (IRES) that we call IRES5’UTR, it can also be translated by an IRES-dependent mode. The IRES-dependent mode enables the full-length mRNA to be translated when the cap-dependent mode is impaired. The activity of the IRES5’UTR is weak in physiological conditions, but it is stimulated when the cell cycle is arrested at the G2/M transition, an arrest induced by HIV-1 infection. A large portion of this IRES, which we name IRES5’UTRc, is present in all HIV-1 mRNAs and its activity is similar to the activity of the complete IRES, which indicates that the IRES-dependent mode can be used by all HIV-1 mRNAs. During my doctoral studies, I investigated how the HIV-1 IRES5’UTR functions. I transfected Jurkat T cells, a lymphocytic cell line derived from the natural target cells of HIV-1, with a dual-luciferase reporter containing the coding sequences of the Renilla luciferase (Rluc) and the firefly luciferase (Fluc) separated by the complete 5’UTR of the HIV-1 full-length mRNA. Translation of Rluc is cap-dependent while translation of Fluc depends on HIV-1 IRES5’UTR. First, I performed a mutational analysis and I discovered three regions that stimulate the activity of IRES5’UTR and a stem-loop that represses its activity, which we named IRENE (IRES negative element). I showed that the repression induced by IRENE is relieved when cells are exposed to oxidative stress, a type of stress caused by HIV-1 infection. We propose that IRENE maintains the IRES5’UTR in a weakly active conformation in physiological conditions. It is known that IRESes are activated by cellular factors, called ITAFs (IRES trans-acting factors). We propose that the IRES5’UTR adopts an active conformation triggered by the binding of an ITAF that is expressed or relocalized during oxidative stress. These results generated a publication (Gendron et al. Nucleic Acids Research, 2011, 39, 902-912). I then decided to study the effect of the viral protein Tat on the IRES5’UTR activity. In addition to its essential role in the transcription of HIV-1 mRNAs, Tat stimulates the cap-dependent translation of HIV-1 mRNAs by interfering with the inhibition of a canonical initiation factor, eIF2, induced by the protein kinase modulated by double-stranded RNA (PKR) and by unwinding the TAR structure present at the 5’end of all HIV-1 mRNAs. Tat also affects the expression of several cellular genes. I showed that the Tat86 and Tat72 isoforms, but not Tat101, stimulate the activity of the IRES5’UTR. This effect is independent of PKR and TAR, but appears to be dependent upon the conformation of Tat. We suggest that Tat could activate a transcription factor that controls the expression of an ITAF of the IRES5’UTR or else that Tat could directly activate such an ITAF. I also showed that PKR stimulates the IRES5’UTR activity, which is surprising since PKR is an antiviral protein. This effect is independent of the inhibition of eIF2 by PKR and could result from the activation of an ITAF. Knowing that IRES5’UTRc, an active portion of IRES5’UTR is present in all HIV-1 RNAs, our hypothesis is that the stimulation of the IRES activity by PKR would allow Tat mRNA to be translated in the beginning of the replication cycle. This would subsequently allow the cap-dependent translation of HIV-1 mRNAs to proceed, which is stimulated by Tat. These results generated a manuscript that is submitted for publication to RNA. Altogether, my results, coupled to data from literature, lead me to conclude that, in the late phases of the replication cycle, the activity of the HIV-1 IRES5’UTR is stimulated by oxidative stress, by the cell cycle arrest in G2/M and by the presence of high amounts of Tat, while cap-dependent translation is impaired. The IRES5’UTR would thus be critical to translate the HIV-1 full-length mRNA. Consequently, the IRES5’UTR would constitute a very interesting target for the development of novel anti-HIV agents.

Pour comprendre les différents rôles que joue la Télémachie dans l’Odyssée d’Homère, il faut explorer à fond le thème de l’identité. La structure de la Télémachie et les rôles accessoires qu’elle joue dans l’Odyssée contribuent à définir l’identité de Télémaque et celle d’Ulysse. À la fin du poème, même si Télémaque a intériorisé et accepté son origine filiale, son rôle social et l’identité qui y est associée sont laissés indéterminés au moment du retour de son père et en sont même la conséquence. Cela peut expliquer le manque de consensus chez les auteurs modernes en ce qui a trait au développement de Télémaque, ou à son statut social et héroïque (i.e. épithète, maturité, etc.). La Télémachie agit à titre d’élément déclencheur de l’initiation de Télémaque dans la vie héroïque mais le processus qui se poursuit, à la fin de l’Odyssée, y est laissé incomplet. L’étape finale, l’incorporation, durant laquelle la communauté reconnaît la nouvelle identité de Télémaque en tant que héros et adulte, prêt à assumer de plus grandes responsabilités, n’est pas présentée dans l’œuvre d’Homère. / One can understand the various functions of the Telemacheia within the Odyssey only by taking into consideration the identity theme. The structure of the Telemacheia and the accessory functions it plays within the Odyssey contribute to defining Telemachus’ own identity as well as Odysseus’. At the end of the poem, even though Telemachus has internalized and accepted his filial origin, his social role and identity are left undefined at the moment of his father’s return and as a consequence thereof. This may explain the lack of consensus among scholars with regard to Telemachus’ development, or social and heroic status (i.e. epithet, maturity, etc.). The Telemacheia triggers Telemachus’ initiation into heroic life but the process is left incomplete. The final step, incorporation, during which everyone recognizes Telemachus’ new identity as a hero and adult, ready to assume higher responsibilities, is not enacted by the poem.

L’œuvre de JMG Le Clézio se caractérise par sa perpétuelle évolution. Elle échappe aux classifications génériques et maintient son statut subversif et indépendant. L’écriture de cet écrivain traduit les diverses influences qui l’ont marqué, les problèmes auxquels il fait face et la thématique majeure dans laquelle il inscrit son œuvre. À travers l’étude de La quarantaine, paru en 1995, nous essayerons lors du premier chapitre de comprendre comment Le Clézio réinvente son écriture pour remédier au problème de l’impureté du langage qui caractérisait son œuvre d’avant les années quatre-vingts. Dans le deuxième chapitre, nous analyserons les thématiques littéraire, familiale et historique qui font de cet ouvrage un roman de filiation. La quarantaine insiste sur l’importance de l’altérité traditionnelle et non occidentale en tant que facteur dans ce changement romanesque, et dont le mode de vie réfléchit différemment le problème de l’identité chez l’individu occidental. Dans le troisième chapitre, nous aborderons la question des enjeux de l’identité à travers l’expérience initiatique à laquelle se livre le protagoniste de La quarantaine en quête d’un devenir identitaire, d’une émancipation qui réconcilie l’individu moderne avec soi-même. / The work of JMG Le Clézio can be characterised by its perpetual evolution. It defies standard classification, maintaining a subversive and independent status. This writer’s work reflects a diversity of influences that have marked him, the challenges he has faced, and the major themes in which he has set his writing. In the first chapter examining the 1995 publication, La quarantaine, we will discuss Le Clézio’s reinvention of his own writing, in order to resolve the problem of impurities in the language that characterized his earlier work, prior to the 1980s. In the second chapter of this study, literary, familial and historic themes that mark this novel as a “filiation story” will be analysed. This shift in literary style is demonstrated in La quarantaine by its insistence on the importance of the “other,” traditional people of non-western culture; their lifestyle prompts reflection on the identity crisis of the western individual. In the third chapter of this study we will address the identity issues raised in Le Clézio’s novel through an initiation experience in which the protagonist in La quarantaine is engaged at a time of significant rebirth in his life. His quest is for self-actualisation, for an emancipation that will serve to reconcile the modern individual with himself.