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Etude des régulations génétiques et épigénétiques de l'expression des gènes d'ARNr 5S chez Arabidopsis thaliana

Abstract : In Arabidopsis thaliana, polymerase III-transcribed 5S rRNA genes are present at about 1000 copies clustered at pericentromeric heterochromatin of chromosomes 3, 4 and 5. The chromosome 5 bears one 5S rDNA locus on each arm. Transcribed 5S rRNA genes are only present on chromosome 4 and in the large locus of left arm of chromosome 5. In Arabidopsis, 5S rRNA pool is heterogeneous and characterized by the existence of both a major 5S rRNA (more than 90% of total 5S rRNAs) and some minor 5S rRNAs, differing from the major one by one or two base substitutions. Within the framework of the study of the genetic regulation of the 5S rDNA expression, we have identified, cloned and characterized the transcription factor TFIIIA from Arabidopsis that is specific of the 5S genes. We also identified an alternatively spliced product from the TFIIIA gene, named TFIIIAbis, that is shorter than TFIIIA in its N-terminal extremity. The data obtained by the targeting of TFIIIAbis by a RNAi technique and in vitro transcription experiments, suggest a positive effect of TFIIIAbis on the 5S rRNA global rate, probably by stabilizing these RNA. We also studied the epigenetic regulation of the 5S rDNA demonstrating the implication of DNA methylation in the silencing of minor 5S genes. In addition, MOM1 mediates DNA methylation-independent silencing of these genes. We identified a novel transcript originating from 5S genes, named 5S-210 rRNA. As minor 5S rRNA, the expression of the 5S-210 transcripts is under the control of DNA methylation and of the MOM1 pathway. Finally, we demonstrated that all highly repetitive heterochromatic sequences with the exception of transposable elements are controlled by these two distinct epigenetic silencing pathways.
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Submitted on : Wednesday, May 16, 2012 - 4:29:33 PM
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  • HAL Id : tel-00698524, version 1



Isabelle Vaillant. Etude des régulations génétiques et épigénétiques de l'expression des gènes d'ARNr 5S chez Arabidopsis thaliana. Génétique humaine. Université Blaise Pascal - Clermont-Ferrand II, 2006. Français. ⟨NNT : 2006CLF21672⟩. ⟨tel-00698524⟩



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