tRNA Genes Affect Multiple Aspects of Local Chromosome Behavior.

[摘要] In eukaryotic organisms the tRNA genes, which exist in multiple copies, arespread throughout the genome. Although it had been assumed that these genes are spreadthroughout the nucleus, it has recently shown that tRNA genes are actually clustered atthe nucleolus. Since the tRNA genes seem to play a role in organizing the entiregenome, their transcription may have dramatic influences. The three studies presentedhere were undergone to provide insight into these influences and their maintenance.The first study provides evidence that tRNA gene transcription influencesrecombination in the genome. The study examined two different circumstances. Thefirst situation was used to tested if the transcription of repetitive tRNA genes influencedtheir tendency to undergo homologous recombination and the second situation was usedto test how a tRNA gene influences the homologous recombination of two nearbyrepetitive sequences. It was determined that two transcriptionally active tRNA genes hada five times greater rate of recombination than if one or both tRNA genes wereinactivated, however tRNA gene transcription had no discernible influence over therecombination between nearby repetitive elements. This could have implications in thehuman genome, which contains over 1 million RNA polymerase III transcribed SINEelements.The second study explores how tRNA gene transcription influences theirclustering and localization at the nucleolus. This study demonstrated that the condensincomplex associates with tRNA genes and physically interacts with RNA polymerase IIItranscription factors. Condensin’s interactions with these two elements may lead to theclustering and localization of the tRNA genes, which could play an important role in theorganization of the entire genome in eukaryotes.The third study found a gene deletion, mod5Δ, that results in the alleviation ofsilencing near tRNA genes. The results of this study indicate that Mod5p’s catalyticactivity is necessary for tgm silencing. The protein was also shown to be present at tRNA genes and seems to maintain the silencing in cis. These results indicate thatMod5p performs an activity necessary for the repression of pol II transcription and thismay have implications for the regulation of many genes inhigher eukaryotes.

[发布机构] University of Michigan

[效力级别] Recombination

[关键词] TRNA Gene Mediated Repression;Recombination;Molecular;Cellular and Developmental Biology;Science;Cellular & Molecular Biology