Nop17p e Rsa1p são proteínas nucleolares em Saccharomyces cerevisiae, as quais foram identificadas pela sua associação a dois complexos celulares: os snoRNPs de box C/D, através de interação com as subunidades Nop58p e Snu13p, respectivamente, e o R2TP/Hsp90p. Nop17p parece ser responsável por direcionar a chaperona Hsp90p durante a montagem dos snoRNPs, e a associação de Rsa1p a estes complexos ainda não tem uma função estabelecida. Neste trabalho, nós mostramos que a ausência de ambas as proteínas afetam a estabilidade da proteína Nop58p dos snoRNPs e afetam a localização do snoRNA U3. Em relação à ordem de interação das proteínas do core de snoRNps de box C/D, Nop17p associa-se de maneira transiente a Nop1p/Snu13p, seguida da ligação de Nop58p ao complexo. Quanto à rede de interação do R2TP, obtivemos o mutante Nop17(N307S), que não mais interage com Tah1p. Este mutante interage com a subunidade Rvb1p do R2TP, mas não se associa com outras proteínas parceiras de Nop17p(WT). Apesar da importância da interação Nop17p-Tah1p, sua interrupção não afeta o crescimento celular, o que sugere a possibilidade de outro fator estar envolvido na associação entre Nop17p e Hsp90p. / Nop17p and Rsa1p are Saccharomyces cerevisiae nucleolar proteins, which were identified for its association with two cellular complexes: box C/D snoRNPs, through interaction with the core subunits Nop58p and Snu13p respectively, and the R2TP/Hsp90p. Nop17p seems to be responsible for directing Hsp90p to the assembly of snoRNPs. The Rsa1p association to these complexes still have no defined function. In this work, we showed that both proteins absence affect Nop58p stability and causes a mislocalization of the U3 snoRNA. Relativel to the order of assembly of the box C/D snoRNPs core proteins, Nop17p associates transiently with Nop1p/Snu13p, followed by the Nop58p joining to the complex. To study in more detail the protein interactions within the R2TP complex, we obtained the Nop17(N307S) mutant, which no longer interacts withTah1p, but still interacts withRvb1p, another R2TP subunit. Nop17(N307S) does not interact with other Nop17p(WT) partners. Despite the importance of the Nop17p-Tah1p association, the disruption of this interaction does not affect cell growth, suggesting the involvement of a second factor on the Nop17p and Hsp90p association.

De nombreuses fonctions cellulaires essentielles telles que la traduction, l'épissage, la biogenèse des ribosomes et la réplication des télomères font appels aux particules RNP non codantes. La biogenèse de ces dernières chez les eucaryotes est un processus très complexes qui fait intervenir de nombreux facteurs cellulaires. La biogenèse du ribosome nécessite au moins 150 facteurs. Ceux-ci sont importants pour faciliter mais également contrôler la biogenèse de cette machinerie cellulaire essentielle qu'est le ribosome. Parmi ces facteurs, nous avons les snoRNP à boîtes C/D. Ces RNP sont impliqués dans la maturation des pré-ARNr (méthylation post-transcriptionnelle des riboses et clivages endonucléolytiques). Récemment notre laboratoire a participé à la découverte de facteurs d'assemblage de ces RNP. Il s'agit entre autre des protéines Rsa1p, du complexe R2TP (Rvb1p, Rvb2p, Tah1p et Pih1p) et de Hit1p chez la levure Saccharomyces cerevisiae. En utilisant une approche de co-expression à haut débit, nos travaux ont révélé un réseau complexe d'interactions entre les protéines constitutives des snoRNP et leurs facteurs d'assemblage. Couplé à une stratégie de protéolyse ménagée, la co-expression nous a permis d'obtenir des sous-complexes protéiques Snu13p/Rsa1p et Rsa1p/Hit1p qui font actuellement l'objet d'une étude structurale par RMN. En collaboration avec l'équipe de F. Allain (ETH Zurich), nous avons également déterminé la structure tridimensionnelle de la protéine Tah1p, ainsi que de son complexe avec le peptide C-terminale de la protéine chaperonne Hsp90 à haute résolution. Ces travaux ont révélé un mode d'association particulier entre le domaine TPR de la protéine et le peptide / A lot of essential cellular functions like translation, splicing, ribosome biogenesis and telomere replication need the activity of non coding RNPs. The biogenesis of non coding RNPs in eukaryotes is a complex pathway involving numerous cellular factors. For instance, ribosome biogenesis requires more than 150 factors. They are important to facilitate and to control the biogenesis of this essential cellular machinery. These factors include the C/D box snoRNPs. These RNPs are involved in pre-rRNA maturation (post-transcriptional ribose methylation and endo-nucleolytic cleavages). Recently, our laboratory participated to the discovery of snoRNP assembly factors: the Rsa1p protein, R2TP complex (Rvb1p, Rvb2p, Tah1p and Pih1p) and Hit1p in the yeast Saccharomyces cerevisiae. Using a high throughput co-expression approach, we deciphered a network of interactions between RNP core proteins and the assembly factors. Coupled with a limited proteolysis strategy, the co-expression method allowed us to obtain proteins sub-complexes Snu13p/Rsa1p and Rsa1p/Hit1p which are currently studied by NMR. In collaboration with the F. Allain team (ETH Zurich), we also determined the tridimensional structure of protein Tah1p and its complex with the chaperon Hsp90 C-terminal peptide at high resolution. The data obtained reveal a particular mode of association of the Tah1p TPR domain with the Hsp90 peptide

Chez les eucaryotes, la biogenèse des ribosomes débute dans le nucléole par la maturation et la modification des ARN ribosomiques (ARNr), et fait intervenir des centaines de particules ribonucléoprotéiques (RNP) distinctes, comme les petites RNP nucléolaires (snoRNP) à boîtes C/D, qui portent une activité méthyl transférase ciblée sur la position 2’-OH des riboses. Leur biogenèse nécessite l’intervention transitoire de facteurs protéiques constituant une machinerie d’assemblage spécifique. Mon travail de thèse a visé à étudier le rôle fonctionnel de deux de ces facteurs chez la levure S. cerevisiae les protéines Hit1 et Bcd1. Hit1p avait été trouvée au laboratoire être impliquée dans la biogenèse des snoRNP à boîtes C/D, et il était connu que l’expression de Bcd1p est essentielle à la viabilité cellulaire et pour la stabilité des snoRNA à boîtes C/D. Lors de ce travail, nous avons retrouvé le domaine fonctionnel de Hit1p et identifié les acides aminés impliqués dans l’interaction avec Rsa1p, un autre facteur d’assemblage. Par une approche similaire, nous avons recherché les domaines nécessaires à la fonctionnalité de Bcd1p. Le mécanisme par lequel Bcd1p influence spécifiquement les taux de snoRNA à boîtes C/D reste inconnu, mais au cours de ce travail j’ai identifié un nouveau partenaire potentiel pour cette protéine - la chaperonne d’histone Rtt106p. La dernière partie de mon travail a visé à rechercher le lien fonctionnel entre Rtt106p et l’expression des snoRNA à boîtes C/D / In eukaryotes, ribosome biogenesis begins in the nucleolus, by maturation and modification of ribosomal RNAs (rRNA) and involves hundreds of distinct ribonucleoprotein particles, like box C/D small nucleolar RNPs (snoRNPs). Their assembly requires the transient intervention of protein factors constituting a specific assembly machinery. My PhD work aimed to investigate the functional role of two such factors, Bcd1p and Hit1p, in the yeast S. cerevisiae. Hit1p involvement in box C/D snoRNP biogenesis was revealed in our lab, and it was known that Bcd1p expression is essential to cell viability and box C/D snoRNA stability. During this work, we identified the functional domain of Hit1p, and the aminoacids involved in its interaction with Rsa1, another assembly factor. By a similar approach we identified the functional domains of Bcd1p. The mechanism by which Bcd1p specifically influences box C/D snoRNA levels is unknown. However, I identified a potentially new partner for this protein – the Rtt106p histone chaperone. The last part of my work aimed to search for a functional link between this histone chaperone and box C/D snoRNA expression

Nop17p e Rsa1p são proteínas nucleolares em Saccharomyces cerevisiae, as quais foram identificadas pela sua associação a dois complexos celulares: os snoRNPs de box C/D, através de interação com as subunidades Nop58p e Snu13p, respectivamente, e o R2TP/Hsp90p. Nop17p parece ser responsável por direcionar a chaperona Hsp90p durante a montagem dos snoRNPs, e a associação de Rsa1p a estes complexos ainda não tem uma função estabelecida. Neste trabalho, nós mostramos que a ausência de ambas as proteínas afetam a estabilidade da proteína Nop58p dos snoRNPs e afetam a localização do snoRNA U3. Em relação à ordem de interação das proteínas do core de snoRNps de box C/D, Nop17p associa-se de maneira transiente a Nop1p/Snu13p, seguida da ligação de Nop58p ao complexo. Quanto à rede de interação do R2TP, obtivemos o mutante Nop17(N307S), que não mais interage com Tah1p. Este mutante interage com a subunidade Rvb1p do R2TP, mas não se associa com outras proteínas parceiras de Nop17p(WT). Apesar da importância da interação Nop17p-Tah1p, sua interrupção não afeta o crescimento celular, o que sugere a possibilidade de outro fator estar envolvido na associação entre Nop17p e Hsp90p. / Nop17p and Rsa1p are Saccharomyces cerevisiae nucleolar proteins, which were identified for its association with two cellular complexes: box C/D snoRNPs, through interaction with the core subunits Nop58p and Snu13p respectively, and the R2TP/Hsp90p. Nop17p seems to be responsible for directing Hsp90p to the assembly of snoRNPs. The Rsa1p association to these complexes still have no defined function. In this work, we showed that both proteins absence affect Nop58p stability and causes a mislocalization of the U3 snoRNA. Relativel to the order of assembly of the box C/D snoRNPs core proteins, Nop17p associates transiently with Nop1p/Snu13p, followed by the Nop58p joining to the complex. To study in more detail the protein interactions within the R2TP complex, we obtained the Nop17(N307S) mutant, which no longer interacts withTah1p, but still interacts withRvb1p, another R2TP subunit. Nop17(N307S) does not interact with other Nop17p(WT) partners. Despite the importance of the Nop17p-Tah1p association, the disruption of this interaction does not affect cell growth, suggesting the involvement of a second factor on the Nop17p and Hsp90p association.

Les protéines de la famille L7Ae sont les constituants de nombreuses RNP essentielles. Chez les vertébrés, les particules snoRNP C/D et H/ACA sont impliquées dans la biogenèse des ribosomes, la UsnRNP U4 dans l'épissage des pré-ARNm, le complexe télomérase dans la réplication des télomères, et les mRNP SECIS dans la traduction des sélénoprotéines. Comme c'est le cas pour la majorité des RNP eucaryotes, leur assemblage, sous forme d'entités fonctionnelles, ne constitue pas un processus autonome et requiert l'intervention de facteurs spécialisés. En basant notre étude sur l'assemblage des snoRNP C/D, dans l'organisme modèle Saccharomyces cerevisiae, et en utilisant des approches de biologie moléculaire, de biochimie et de génétique, nous avons entrepris de caractériser ces événements. Nos travaux ont contribué à identifier un ensemble de protéines, agissant de façon coordonnée au sein d'une machinerie conservée entre la levure et l'homme. Cette dernière est composée de deux principales sous-unités : (i) Rsa1p/NUFIP, une protéine plate-forme, qui interagit avec certaines protéines de la famille L7Ae et facilite l'assemblage des RNP, (ii) le complexe R2TP (Rvb1p/TIP49, Rvb2p/TIP48, Pih1p/PIH1, Tah1p/SPAGH), qui pourrait opérer des remodelages conformationnels nécessaires à la formation des RNP matures. En plus de ces acteurs centraux, d'autres facteurs sont apparus intimement liés à ce mécanisme. La protéine Hit1p/TRIP3, interagit notamment avec Rsa1p/NUFIP et s'est avéré requise pour assurer sa stabilité chez la levure. La chaperonne HSP90, dont le rôle est prédominant chez l'homme, exerce son activité sur certains constituants des RNP. Enfin, la protéine Bcd1p/BCD1 pourrait être associée à cette machinerie dans le cadre spécifique de l'assemblage des snoRNP C/D / The L7Ae family proteins are essential components of many RNPs. In vertebrates, C/D and H/ACA snoRNPs are involved in ribosome biogenesis, the U4 snRNP in pre-mRNA splicing, the telomerase complex in telomeres replication, and mRNP SECIS in selenoproteins translation. Like most eukaryotic RNPs, assembly in functional entities is not an autonomous process and requires the intervention of specialized factors. Basing our study on the assembly of C/D snoRNP in the model organism Saccharomyces cerevisiae, and using approaches of molecular biology, biochemistry and genetics, we undertook to decipher these mechanisms. Our work has helped to identify a set of proteins, acting in a coordinated manner within a machinery conserved between yeast and human. This machinery consists of two major subunits: (i) Rsa1p/NUFIP, a platform protein that interacts with some proteins of the L7Ae family and facilitates the RNPs assembly, (ii) the R2TP complex (Rvb1p/TIP49, Rvb2p/TIP48, Pih1p/PIH1, Tah1p/SPAGH), which could induce conformational remodeling necessary for the formation of mature RNPs. In addition to these key players, other factors appeared closely linked to this mechanism. The Hit1p/TRIP3 protein interacts with Rsa1p/NUFIP and is required to ensure its stability in yeast. HSP90 chaperone, whose role is predominant in human, operates on some components of the RNPs. Finally, the Bcd1p/BCD1 protein is associated specifically with this machinery during C/D snoRNPs assembly