Homeobox genes encode homeodomain (HD) proteins which function as transcription factors and play an important role in plant and animal development by controlling cell specification and pattern formation. (Knotted1 in Arabidopsis thaliana) KNAT1-like mRNAs referred to as PtKN1(HD+) and mRNA sequences which lack HD region referred as PtKN1(hd-) were cloned from embryos of loblolly pine (Pinus taeda L.). Production of PtKN1(hd-) mRNAs is developmentally regulated and their encoded protein is abundant in mature pine embryos. Both forms of PtKN1 are produced by the same gene which has 5 exons; the regulatory dynamic is between cleavage-polyadenylation or termination within intron 3 to produce PtKN1 mRNA lacking HD sequences and splicing of exon 3 to exon 4 which excludes the 3'UTR/exon3 sequence to create an mRNA which encodes a HD. KNAT1 mRNA in Arabidopsis which lacks HD sequences was identified and characterized. While KNAT1 has been studied for many years, this is the first report of a KNAT1 mRNA lacking HD. KNAT1 mRNA lacking HD sequences was identified for the RS1 gene of maize, a monocotyledon. This is the first report of splicing of KNAT1 genes to produce mRNAs lacking HD sequences. The phenomenon appears to be ubiquitous as it is observed in gymnosperms, and both dicotyledonous and monocotyledonous angiosperms.

Thesis (Ph. D.)--University of Washington, 2000. / Vita. Includes bibliographical references (leaves 73-77).

We investigated the effect of pyridoxine supplementation on the utilization of protein in a low-protein, plant-based diet in four subjects (2 men and 2 women), aged 21 to 38 years. Following two days of a negligible protein diet, this 34 day study was divided into three dietary periods: the subjects received a low-protein, plant-based diet during period I for 10 days (no pyridoxine supplement), the same diet but with the addition of 50 mg pyridoxine HCl during period II for 7 days, and their self-chosen diets during period III for 15 days (no pyridoxine supplement). Data for period III will be reported elsewhere. The greatest portion of protein in the experimental diet was furnished by pinto beans (1.02 g nitrogen) and peanut butter (0.86 g nitrogen); nitrogen intake was kept constant at 4.56 g/d for the men and 4.15 g/d for the women during periods I and II. These diets administered during periods I and II provided 0.907 mg of vitamin B-6 for the men and 0.758 mg of vitamin B-6 for the women and was adequate in other nutrients except for protein. Overall, the effect of 50 mg pyridoxine HC1 supplementation on the utilization of protein in a low-protein plant-based diet was not statistically significant (p > 0.05) on the basis of a paired t-test for the parameters measured: nitrogen balance, apparent protein digestibility, as well as plasma and urinary urea nitrogen. Furthermore, we obtained conflicting results, when the subjects received pyridoxine, their plasma urea nitrogen increased slightly (suggesting increased protein degradation), while the percent of total urinary nitrogen excretion as urea nitrogen decreased (suggesting decreased protein degradation). These changes were not statistically significant, but limitations in the nitrogen balance technique and the analytical procedures we used may have contributed to these conflicting results. We suggest that a longer study with more subjects may show a greater improvement of plant protein utilization than we had observed. / Graduation date: 1990

Il serait opportun de débuter cette introduction en donnant une définition claire du processus d'édition des ARN, mais c'est aussi un exercice périlleux car le terme d'édition des ARN a été utilisé dans la littérature pour décrire une multitude de processus biochimiques différents et la distinction entre les processus d'édition ou de modification est parfois confuse. Le terme d’édition des ARN a été utilisé pour la première fois en 1986 pour décrire l’insertion de 4 résidus uridines dans le transcrit mitochondrial coxII chez le trypanosome (Benne et al., 1986). La communauté scientifique était sceptique et on a alors pensé que ce mécanisme était sans doute spécifique à ce « drôle » de protozoaire. Puis, rapidement, l'édition d'ARNm a été décrite chez de nombreux organismes eucaryotes, soit pour expliquer des processus d'insertions ou de délétions de nucléotides (qui altèrent le nombre de nucléotides contenus dans la molécule d'ARN) soit pour décrire des conversions ou des remplacements de nucléotides (qui altèrent l'identité des nucléotides contenus dans la molécule d'ARN). Plus tard, le terme d'édition des ARN a été utilisé pour décrire des désaminations (le plus fréquemment C-en-U, et A-en-I) survenant dans les ARNt et les ARNr d'organismes eucaryotes et procaryotes, mais aussi des modifications mineures des résidus (comme l'ajout de groupement méthyl). De même la polyadénylation de la partie 3' de certains ARNt est aussi communément appelée processus d'édition des ARN. Enfin, un phénomène d'édition cotranscriptionnel des ARN lié au « patinage » de l'ARN polymérase a également été mis en évidence chez certains virus.

Bibliography: leaves 138-158. / x, 158 leaves : ill. ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / This study identified and investigated the properties, functions and patterns of accumulation of prominent berry proteins associated with white wine haze. Detailed analysis was conducted on two PR-like proteins of V. vinifera, VVPR-4a and VVTL1. In vitro fungal growth inhibition assays suggested that berry PR-like proteins may play an important role in plant defence, particularly against fungal attack. Results of this study also have future implications for controlling the ripening process of grapes. / Thesis (Ph.D.)--University of Adelaide, Dept. of Horticulture, Viticulture and Oenology, 1999

Diss. (sammanfattning) Linköping : Linköpings universitet, 2006. / Härtill 5 uppsatser.

Diss. (sammanfattning) Linköping : Univ., 2006. / Härtill 4 uppsatser.

FundaÃÃo Cearense de Apoio ao Desenvolvimento Cientifico e TecnolÃgico / O feijÃo-caupi [Vigna unguiculata (L.) Walp] à uma importante leguminosa devido ao seu potencial nutricional, revelado principalmente pelo alto teor de proteÃnas. As proteÃnas apresentam destaque nas propriedades funcionais (tecnolÃgicas) e o interesse por novas fontes proteicas a custos acessÃveis, leva ao crescente estudo das leguminosas. Assim, o presente trabalho objetivou a obtenÃÃo de isolados proteicos de dois genÃtipos de feijÃo-caupà (Cauamà e Tumucumaque), bem como a caracterizaÃÃo bioquÃmica e funcional destes isolados e de suas sementes. Os resultados mostraram que as sementes dos genÃtipos estudados sÃo boas fontes de proteÃnas (23,19 a 24,02%), fibras (17,75 a 19,78%) e apresentam baixo teor de lipÃdeos (1,67%). Os isolados proteicos obtidos apresentaram elevado teor proteico (> 90%) e rendimento (35,11 e 38,12%, respectivamente Tumucumaque e CauamÃ). Tanto os isolados como as sementes nÃo se mostraram tÃxicos, mas apresentraram inibidores de tripsina (24,2 a 28,2 UI/ Âg de proteÃna), quimiotripsina (26,66 a 32,17 UI/ Âg de proteÃna) e lectina (80.000 a 320.000 UI/ Âg de proteÃna). A digestibilidade dos isolados (63,23 a 63,81%) foi superior a das sementes (50,07 a 54,37%). A fraÃÃo proteica predominante foi a globulina, com maior concentraÃÃo nos isolados. A solubilidade das sementes e isolados apresenta-se em formato de U, com menor solubilidade no ponto isoelÃtrico. Os isolados proteicos apresentaram melhor capacidade de absorÃÃo de Ãgua (2,41 a 2,44 ml/g de amostra), de Ãleo (2,38 a 2,8 1ml/g de amostra) e formaÃÃo de gel (8 a 10%). Jà as sementes apresentaram maior formaÃÃo de espuma (52,66 a 57,89%). Assim, pode-se concluir que os isolados proteicos obtidos desse genÃtipo sÃo promissores para aplicaÃÃo nutricional, por apresentarem elevado teor proteico (> 90%), razoÃvel digestibilidade (>60%) e perfil de aminoÃcidos. Da mesma forma, sÃo promissores para a aplicaÃÃo tecnolÃgica, uma vez que se destacaram nas propriedades de solubilidade, capacidade de absorÃÃo de Ãgua e de Ãleo e formaÃÃo de gel. Assim, os isolados proteicos podem ser utilizados como ingredientes de produtos alimentÃcios, contribuindo com o aumento do valor nutricional dos alimentos e agregando valor aos genÃtipos melhorados do feijÃo-caupi. / The cowpea (Vigna unguiculata (L.) Walp) is an important plant due to their nutritional potential, revealed to mainly high protein content. The highlight proteins present in the functional properties (technological) and interest in new sources of protein at affordable costs leads to increasing interest in studying the legume. Thus, the present study aimed to obtain protein isolates from bean cowpea genotypes, as the biochemical and functional characterization of these isolates and their seeds. The results showed the seeds are good sources of protein (23.19 to 24.02%), fiber (17.75 to 19.78%) and have a low lipid content (1.67%). The protein isolated obtained showed high purity (above 90%) and yield (35.11 and 38.12%). Both isolated as seeds not proved toxic but exhibited trypsin inhibitor (24.2 to 28.2 IU), chymotrypsin (26.66 to 32.17 IU) and lectin (80.000-320.000 IU). The digestibility of isolated (63.23 and 63.81%) was higher than the seeds (50.07 to 54.37%). The predominant proteic fraction was globulin, with the highest concentration in the isolates. The seeds and isolated solubilities presents U-shaped, with lower solubility at the isoelectric point. The isolated protein showed greater capacity for absorb water (2.41 to 2.44 ml/g sample), oil (from 2.38 to 2.81 ml / g sample) and gel concentrations (8-10%). Already seeds showed higher foaming (52.66 to 57.89%).

FundaÃÃo Cearense de Apoio ao Desenvolvimento Cientifico e TecnolÃgico / O lÃtex da planta lactÃfera Calotropis procera (Ait.) R. Br. à um composto biologicamente ativo importante que apresenta propriedades relevantes como as atividades antiinflamatÃria e antidiarrÃica, embora jà tenha sido previamente mostrado que esse lÃtex produz efeitos tÃxicos considerÃveis em animais. Um outro fato à que nÃo à sabido, ainda, se as proteÃnas do lÃtex de C. procera produzem efeitos alergÃnicos, assim como as proteÃnas do lÃtex de Hevea brasiliensis. O potencial do lÃtex como um fÃrmaco, por essa razÃo, depende da separaÃÃo das propriedades curativas das propriedades tÃxicas e alergÃnicas, mas nÃo existe investigaÃÃo cientÃfica nessa Ãrea. O presente estudo teve como objetivo investigar aspectos bioquÃmicos, toxicolÃgicos e alergÃnicos do lÃtex da planta C. procera, atravÃs do estudo da digestibilidade in vitro e in vivo, avaliaÃÃo da toxicidade subcrÃnica e aguda por via oral e anÃlise da induÃÃo de resposta imune pelas vias subcutÃnea e oral das suas fraÃÃes. O lÃtex foi fracionado em trÃs fraÃÃes distintas de acordo com a sua solubilidade em Ãgua e tamanho molecular. As fraÃÃes foram assim denominadas: proteÃnas do lÃtex (PL), correspondendo Ãs principais proteÃnas do lÃtex; proteÃnas da diÃlise (PD), representando as substÃncias de baixa massa molecular; e borracha do lÃtex (BL) que à altamente insolÃvel em Ãgua. A fraÃÃo PL foi investigada, com relaÃÃo a alguns aspectos bioquÃmicos, como seu perfil protÃico por PAGE-SDS e anÃlise da composiÃÃo de seus aminoÃcidos. As proteÃnas do lÃtex tambÃm foram submetidas à digestÃo in vitro com as enzimas proteolÃticas pepsina, tripsina, quimiotripsina e protease de Streptomyces griseus e a digestibilidade in vitro foi avaliada por cromatografia de filtraÃÃo em gel ou PAGE-SDS. A digestibilidade in vivo de PL foi analisada quando animais experimentais ingeriram essa fraÃÃo por 35 dias. O volume de PL consumido foi registrado diariamente e amostras das fezes dos animais coletadas, tratadas e submetidas à PAGE-SDS e ensaios de imunodifusÃo radial dupla de Ouchterlony, com anticorpos policlonais contra PL. Com relaÃÃo aos aspectos toxicolÃgicos, a fraÃÃo PL foi oralmente administrada a animais experimentais por 35 dias, para a avaliaÃÃo da toxicidade subcrÃnica. Aumentos na massa corpÃrea foram registrados e amostras sangÃÃneas foram analisadas semanalmente. ApÃs o perÃodo experimental, os animais foram sacrificados e um nÃmero de parÃmetros bioquÃmicos e fisiolÃgicos foram determinados. Esses incluÃram determinaÃÃes sÃricas de glicose sangÃÃnea, colesterol total, HDL-colesterol, triglicerÃdeos, testes da funÃÃo hepÃtica (proteÃnas totais, albumina, alanina aminotransferase â ALT e aspartato aminotransferase â AST), testes da funÃÃo renal (urÃia e creatinina), contagens total e diferencial de leucÃcitos sangÃÃneos e do fluido peritonial e anÃlise das proteÃnas sÃricas por PAGE-SDS. Os animais tiveram seus ÃrgÃos vitais (fÃgado, rins, baÃo, intestino delgado, intestino grosso, pÃncreas e estÃmago) dissecados e as massas frescas relativas foram determinadas. Na avaliaÃÃo da toxicidade aguda, a fraÃÃo PL foi administrada por via oral a animais experimentais e a monitoraÃÃo de alteraÃÃes comportamentais desses animais tambÃm foi realizada. Quanto aos aspectos alergÃnicos, respostas imunolÃgicas do lÃtex de C. procera foram investigadas pelas vias oral e subcutÃnea em camundongos. Anti-soros contra as fraÃÃes PL, PD e BL foram analisados quanto a IgG e IgA por ELISA, enquanto IgE e IgG1 foram monitoradas por anafilaxia cutÃnea passiva (PCA) em ratos e camundongos, respectivamente. Os perfis protÃicos das fraÃÃes PL e BL foram analisados por PAGE-SDS. Com relaÃÃo aos resultados dos aspectos bioquÃmicos, a fraÃÃo PL possui uma quantidade apreciÃvel de proteÃnas, baixo conteÃdo de aminoÃcidos sulfurados (metionina e cisteÃna) e um nÃmero considerÃvel de aminoÃcidos (arginina, lisina, fenilalanina e tirosina) que representam sÃtios de clivagem para as enzimas proteolÃticas animais usadas. A fraÃÃo PL foi digerida pela aÃÃo da pepsina, tripsina e quimiotripsina como revelado por anÃlises de filtraÃÃo em gel e PAGE-SDS. A digestÃo completa das proteÃnas do lÃtex foi facilmente obtida pelo tratamento com a protease de S. griseus. Anticorpos policlonais de coelho produzidos contra PL nÃo apresentaram reaÃÃo cruzada com as molÃculas presentes nas fezes dos ratos experimentais. PadrÃes semelhantes de eletroforese foram observados para as quantidades desprezÃveis de proteÃna observadas nos materiais fecais dos animais controle e experimentais. Quanto aos resultados da avaliaÃÃo da toxicidade subcrÃnica, nenhuma morte foi observada durante o experimento. Animais controle e experimentais apresentaram taxa de crescimento semelhante e os ÃrgÃos vitais exibiram massas frescas relativas similares. As funÃÃes hepÃtica e renal, parÃmetros glicÃmicos e lipidÃmicos sÃricos situaram-se em nÃveis normais. Os padrÃes protÃicos eletroforÃticos dos soros dos animais controle e experimental exibiram perfis muito similares. A fraÃÃo PL nÃo induziu inflamaÃÃo aguda na cavidade peritonial dos ratos, como determinado pelas contagens total e diferencial de leucÃcitos. O resultado mais relevante detectado foi um aparente efeito proliferativo das proteÃnas do lÃtex sobre os linfÃcitos sangÃÃneos que tenderam a aumentar, enquanto os neutrÃfilos permaneceram em nÃvel normal. Deve ser enfatizado que os animais experimentais exibiram comportamento, aspectos morfolÃgicos e bioquÃmicos normais, indicando ser improvÃvel que os mesmos estivessem sob qualquer condiÃÃo patolÃgica ou infecciosa. Portanto, o incremento da populaÃÃo de linfÃcitos no soro sangÃÃneo deve ser atribuÃdo a um efeito notÃvel das proteÃnas do lÃtex e nÃo a qualquer evento prejudicial. A fraÃÃo PL foi incapaz de induzir toxicidade aguda, pois nenhuma mudanÃa comportamental foi observada nos animais experimentais. Com relaÃÃo aos resultados dos aspectos alergÃnicos, nenhuma das fraÃÃes induziu aumentos nos nÃveis de anticorpos, quando os camundongos receberam as fraÃÃes do lÃtex por via oral e, portanto, nÃo desenvolveram alergia. Entretanto, anti-soros de camundongos sensibilizados com PL e BL por administraÃÃo subcutÃnea apresentaram resposta imunolÃgica considerÃvel, e PD nÃo induziu sÃntese de anticorpos. O nÃvel de IgG aumentou consistentemente contra PL e BL, enquanto a resposta de IgA foi detectada unicamente contra PL. PL e BL induziram reaÃÃes de PCA muito fortes, sugerindo que ambas as fraÃÃes contÃm substÃncias do lÃtex envolvidas na alergenicidade. AlÃm disso, a anÃlise protÃica de PL e BL sugere que BL ainda retÃm proteÃnas residuais, co-precipitadas com a borracha, abundantemente encontradas na fraÃÃo PL, que poderiam explicar as alergenicidades semelhantes. Nenhuma reaÃÃo de IgG1 foi detectada em quaisquer dos anti-soros testados. Conclui-se que as proteÃnas do lÃtex foram parcialmente susceptÃveis à proteÃlise em ensaios in vitro e, ou foram digeridas e absorvidas, ou foram absorvidas Ãntegras, quando ingeridas em ensaios in vivo. Eventos tÃxicos ou letalidade associados ao lÃtex, como descritos na literatura, nÃo estÃo relacionados com a fraÃÃo PL. A fraÃÃo PL produziu efeito proliferativo parcial sobre as cÃlulas mononucleadas, principalmente linfÃcitos e nÃo induziu resposta inflamatÃria aguda, quando administrada pela via oral. Efeitos alergÃnicos puderam ser detectados, por via subcutÃnea, com as fraÃÃes PL e BL, e nÃo foram observados por via oral. EvidÃncias para uma possÃvel tolerÃncia sistÃmica Ãs proteÃnas do lÃtex por via oral foram fornecidas. As proteÃnas do lÃtex podem atuar como imunoestimulantes. As proteÃnas do lÃtex permanecem uma fonte interessante de molÃculas biologicamente ativas que devem ser estudadas em detalhe quanto Ãs suas propriedades estruturais, funcionais e aplicativas. / The latex of the lactiferous plant Calotropis procera (Ait.) R. Br. is an important biologically active compound that displays relevant properties like antiinflammatory and antidiarrhea activities, although the latex has previously been shown to produce considerable toxic effects on animals. Another question is that it is not known yet whether the latex proteins from C. procera induce allergenic effects, just like the latex proteins from Hevea brasiliensis. The potential of the latex as a pharmaceutical, therefore, depends on separating the curative properties from the toxic and allergenic properties, but there has been a lack of scientific investigation in this area. The objective of the present study was to investigate biochemical, toxicological and allergenic aspects of the latex from the plant C. procera, through the study of in vitro and in vivo digestibility, evaluation of acute and subchronic toxicity by oral route, and analysis of immune response induction by subcutaneous and oral route of its fractions. The latex was fractionated into three distinct fractions according to their water solubility and molecular size. The fractions were named as: latex proteins (LP), corresponding to the major latex proteins; dialysis proteins (DP), representing low molecular size substances; and rubber latex (RL), which was highly insoluble in water. LP fraction was investigated in some biochemical aspects, like its protein profile by SDS-PAGE analysis and its amino acid composition determination. Latex proteins were also subjected to in vitro digestion with trypsin, chemotrypsin, pepsin and Streptomyces griseus protease and in vitro digestibility was evaluated by gel filtration and SDS-PAGE analysis. The in vivo digestibility of LP was analyzed when experimental animals ingested this fraction for 35 days. The volume uptake of LP was recorded daily and samples of fecal material from animals were collected, treated and submitted to SDS-PAGE analysis and radial double immunodifusion assays, with polyclonal antibodies raised against LP. In relation to toxicological aspects, LP fraction was orally administered to experimental animals for 35 days, to allow subchronic toxicity evaluation. Increases in body mass were recorded and blood samples were analyzed weekly. After the test period, the animals were sacrificed and a number of biochemical and physiological parameters determined. These included sera determinations of blood glucose, total cholesterol, HDL-cholesterol, triglycerides, hepatic function tests (total proteins, albumin, alanine aminotransferase â ALT and aspartate aminotransferase â AST), renal function tests (urea and creatinin), total and differential leukocyte counts in blood and peritoneal fluid and analysis of sera proteins by SDS-PAGE. Animals had internal key organs (liver, kidneys, spleen, small intestine, large intestine, pancreas and stomach) dissected and the relative fresh masses were determined. In the acute toxicity evaluation, LP fraction was administered by oral route to experimental animals and behavioral changes in animals were also monitored. With reference to allergenic aspects, immunological responses of latex from C. procera were investigated by oral and subcutaneous routes in mice. Anti-sera against LP, DP and RL fractions were assayed for IgG and IgA titration by ELISA, while IgE and IgG1 were accessed by passive cutaneous anaphylaxis (PCA) in rats and mice, respectively. Protein profiles of LP and RL fractions were analyzed by SDS-PAGE. Concerning biochemical aspects results, LP fraction possesses appreciable amount of protein, low content of sulphurated amino acids (methionine and cysteine) and a considerable number of amino acids (arginine, lysine, phenylalanine and tyrosine) that represent cleavage sites to animal proteolytic enzymes studied. LP fraction was digested by the action of pepsin, trypsin and chemotrypsin as revealed by gel filtration and SDS-PAGE analyses. The full LP digestion was easily achieved by S. griseus protease treatment. Rabbit polyclonal antibodies raised against LP failed to detect cross-reactive molecules in faeces of experimental rats. Similar patterns of electrophoresis were observed for the negligible amounts of protein observed in the fecal materials of control and test animals. With relation to subchronic toxicity evaluation results, no death was observed during the experiment. Experimental and control animals presented similar growth rate and key organs exhibited similar relative fresh masses. Hepatic and renal functions, sera glycemic and lipidemic parameters were determined to be at normal levels. Likewise, the electrophoretic protein patterns of sera from untreated and treated animals exhibited quite similar profiles. Uptake of latex proteins did not induce acute inflammation into peritoneal cavity of rats as determined by the total and differential leukocytes counts. The most relevant result discovered was an apparent proliferative effect of the latex proteins upon blood lymphocytes that tended to increase, whilst neutrophils remained at normal level. It should be emphasized that the experimental rats were normal in their behavior, morphological and biochemical aspects, indicating that it is unlikely that they were under any pathological or infectious condition. Therefore, the increment of lymphocytes population in the blood serum should be attributed to the staking effect of the latex proteins rather than any harmful event. LP fraction was unable of presenting acute toxicity in experimental animals, because no behavioral changes in animals were observed. Concerning allergenic aspects results, none of the fractions induced antibodies level increases when mice received latex fractions by oral route and thus, did not develop allergy. Nonetheless, anti-sera of mice sensitized with LP and RL by subcutaneous administration displayed considerable immunological response, while DP did not induce antibodies synthesis. IgG level augmented consistently against LP and RL, while IgA response was detected to LP solely. LP and RL induced very strong PCA reactions suggesting that both fractions would contain latex substances involved in allergenicity. Furthermore, protein analysis of LP and RL suggests that RL still retain residual proteins, co-precipitated with rubber, abundantly found in LP, that could explain its similar allergenicity. No IgG1 reaction was detected in any of the anti-sera tested. It can be concluded that latex proteins were partially susceptible to digestive proteolysis when accessed by in vitro assays, and were digested and absorbed, or were absorbed in its intact form, when ingested and analyzed by in vivo tests. Toxic events or lethality associated with latex, as described in the literature, are not related to LP fraction. Latex proteins produced partial proliferative effect upon mononuclear cells, mainly lymphocytes and did not induce an acute inflammatory response, when administered by oral route. Allergenic effects could be detected, by subcutaneous route, with LP and RL fractions, and were not observed by oral route. Evidences for an inducible tolerance acquired to latex proteins by oral route were provided. Latex proteins may act as immune stimulants. The proteins from the latex remain an interesting source of biologically active molecules that should be studied in detail for their structural, functional and applicative properties.

O produto do gene thi1 de Arabidopsis thaliana está provavelmente envolvido na biossíntese de tiamina (vitamina B1) e na proteção do DNA organelar contra danos. Estudos sobre a biossíntese da tiamina em plantas sugerem uma localização plastidial para este mecanismo, o que está de acordo com a existência de um peptídeo de trânsito cloroplástico (TP) na região N-terminal de THI1. Por outro lado, em leveduras a tiamina é sintetizada em mitocôndrias. Interessantemente, o cDNA de thi1 de A. thaliana complementa uma cepa de levedura com disrupção no gene homólogo thi4. A análise da seqüência de aminoácidos de THI1 revelou a presença de uma região capaz de formar uma estrutura do tipo a-hélice anfifílica, freqüentemente encontrada em preseqüências mitocondriais, localizada logo após o peptídeo de trânsito cloroplástico. O papel desta região na localização da proteína THI1 nas mitocôndrias foi comprovado a partir de ensaios envolvendo construções de genes quiméricos (contendo ou não a putativa seqüência de direcionamento mitocondrial) e um gene repórter (uidA). Estas construções foram introduzidas em plantas de tabaco e a localização da atividade GUS foi determinada nas frações subcelulares das plantas transgênicas. Análise direta da presença de THI1 nas mitocôndrias e cloroplastos de Arabidopsis foi realizada via imunolocalização. Também foram fornecidas evidências que as duas isoformas organelares são codificadas por um único transcrito nuclear. Experimentos de transcrição/tradução in vitro indicaram a ocorrência de dois produtos da tradução a partir de códons de iníciação em fase de leitura. Mutações sítio-específicas na seqüência de thi1 acoplados à experimentos usando a proteína fluorescente verde (GFP) mostraram que a tradução no primeiro AUG determina a localização da proteína nos cloroplastos, enquanto que a tradução no segundo AUG é responsável pelo endereçamento da proteína às mitocôndrias. A análise do contexto para início da tradução revelou que a região em torno do primeiro AUG é mais favorável para a tradução do mRNA de thi1. Além disso, observou-se a presença de uma forte estrutura em "grampo de cabelo" próximo ao segundo códon AUG, indicando um contexto subótimo capaz de interferir na tradução. Estas observações confirmaram os dados obtidos a partir da tradução in vitro na qual a iniciação se dá preferencialmente no primeiro AUG o que pode sugerir uma maior necessidade da proteína nos plastídeos. / Arabidopsis thaliana thi1 gene product is probably involved in both thiamine biosynthesis as well as protection of organellar DNA from damage. Studies of thiamine biosynthesis in plants suggest a plastid location for the pathway, which is in agreement with the predicted THI1 N-terminal chloroplastic transit peptide (TP). On the other hand, thiamine is synthesized in mitochondria in yeast cells. Interestingly, A. thaliana thi1 cDNA complements a yeast strain disrupted for the homologous thi4 gene. Analysis of THI1 amino acid sequence revealed the presence of a putative amphiphilic a-helix, which is typical for mitochondrial presequences, located downstream of the chloroplast transit peptide. The role of this sequence on mitochondrial import has been shown by chimeric gene constructs (carrying or not the putative mitochondrial presequence) and the uidA reporter gene. These constructions have been introduced into tobacco plants and the GUS activity has been measured in subcellular fractions of transgenic plants. Direct analysis of THIp in mitochondria and chloroplasts has been done via ImmunoGold labelling experiments. Additional evidence suggested that the two organellar isoforms were encoded by a single nuclear transcript. In vitro transcription/translation experiments revealed the presence of two translational products by a differential usage of two in-frame translational start codons. Coupling site-specific mutations on THI1 encoding sequence with green fluorescent protein (GFP) gene fusions showed that translation initiation in the first AUG directs translocation of THI1 to plastids. However, when translation initiates from the second AUG THI1 is addressed to mitochondria. Analysis of the translation efficiency of thi1 mRNA revealed that the best context for translation initiation is present at the first AUG. In addition, it has been shown a suboptimal context at the second AUG and a strong stem-and-loop structure which is likely to slow translation. These observation confirm the in vitro translation data in which translation occurs preferentially in the first AUG, what could suggest a higher requirement of the protein in plastids.