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dc.contributor.advisorBryk, Maryen_US
dc.creatorLi, Chonghuaen_US
dc.date.accessioned2010-01-15T00:05:54Zen_US
dc.date.accessioned2010-01-16T01:18:56Z
dc.date.available2010-01-15T00:05:54Zen_US
dc.date.available2010-01-16T01:18:56Z
dc.date.created2008-12en_US
dc.date.issued2009-05-15en_US
dc.identifier.urihttp://hdl.handle.net/1969.1/ETD-TAMU-3109
dc.description.abstractIn S. cerevisiae, the ribosomal DNA locus is silent for RNA polymerase II (Pol II) transcription and recombination (rDNA silencing). Our goal is to understand how histones and histone-modifying enzymes regulate the silent chromatin at the rDNA locus. Sir2, a NAD+-dependent histone deacetylase, is required for rDNA silencing. To understand how Sir2 regulates rDNA silencing, we performed chromatin immunoprecipitation to measure the association of modified histones across the rDNA repeat in wild-type and sir2Δ cells. We found that in sir2Δ cells, histone H3 at the rDNA became hyperacetylated and hypermethylated. High levels of K4-methylated H3 correlate with Pol II transcription. Consistent with this, we found that the nontranscribed spacer (NTS) region was transcribed by Pol II in sir2Δ cells. To investigate if transcription of the NTS region regulates rDNA silencing, we overexpressed this region both in trans and in cis. Our data showed that overexpression of the NTS region in cis caused Pol II silencing defect and hyperrecombination at the rDNA. These data suggest that Sir2 contributes to maintain the silent chromatin at the rDNA by repressing Pol II transcription in the NTS region. We also found that the NTS transcripts could be translated in vitro and that they copurified with polysomes, suggesting that the transcripts may encode proteins or that the transcripts are somehow involved in the process of translation. Additionally, we examined the role of linker histone H1 in regulating rDNA silencing. We found that, unlike Sir2 that represses both Pol II transcription and recombination, histone H1 only represses recombination at the rDNA. The hyperrecombination defect at the rDNA is more severe in sir2Δ hho1Δ double mutant than in either single mutant, suggesting histone H1 and Sir2 act independently. Consistently, hho1Δ cells did not accumulate extrachromosomal rDNA circles (ERCs) or the Holliday junction intermediates, which accumulate in sir2Δ cells. These data suggest that histone H1 and Sir2 regulate different recombination pathways. In summary, my research has provided insight into the mechanism of how silent chromatin at the rDNA locus is regulated, which will help us understand how fundamental components of chromosomes affect gene expression and genome stability.en_US
dc.format.mediumelectronicen_US
dc.format.mimetypeapplication/pdfen_US
dc.language.isoen_USen_US
dc.subjectrDNA silencingen_US
dc.subjectchromatin structureen_US
dc.subjecthistone modificationen_US
dc.titleThe role of histones and histone modifying enzymes in ribosomal dna silencing in saccharomyces cerevisiaeen_US
dc.typeBooken
dc.typeThesisen
thesis.degree.departmentBiochemistry and Biophysicsen_US
thesis.degree.disciplineBiochemistryen_US
thesis.degree.grantorTexas A&M Universityen_US
thesis.degree.nameDoctor of Philosophyen_US
thesis.degree.levelDoctoralen_US
dc.contributor.committeeMemberHall, Timothy C.en_US
dc.contributor.committeeMemberPolymenis, Michaelen_US
dc.contributor.committeeMemberScholtz, J. Martinen_US
dc.type.genreElectronic Dissertationen_US
dc.type.materialtexten_US
dc.format.digitalOriginborn digitalen_US


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