Chromatin remodelling in Sacchromyces cerevisiae by RSC

• Main Author: Durley, Samuel C.
• Published: Cardiff University 2013
• Subjects: 572.8; QH426 Genetics
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.590335

RSC is a member of the multi-subunit SWI/SNF family of ATPase-dependent chromatin remodellers and it is implicated in transcriptional regulation and DNA repair in Saccharomyces cerevisiae. The central ATPase subunit, Sth1, translocates nucleosomes in vitro and mutations in human RSC sub-unit orthologues are implicated in human disease. RSC is found in two isoforms, defined by the presence of either the Rsc1 or Rsc2 subunits, and these appear to confer distinct remodelling functions in different genomic contexts. At the MAT locus, Rsc1 and Rsc2 appear to mediate different forms of nucleosome positioning which are required for efficient mating type switching. Elsewhere in the genome, it has been suggested that RSC can create partially un-wrapped nucleosomes in order to facilitate transcription factor binding. This thesis uses indirect-end-label analysis and chromatin-sequencing technologies to dissect the chromatin remodelling functions of RSC and to determine the roles of Rsc1, Rsc2 and their subdomains. The work presented here suggests that four chromatin-remodelling outcomes arise from RSC activity. Firstly, RSC alters the positions of a tract of nucleosomes abutting HO endonuclease-induced double-strand DNA breaks both at MAT and non-MAT loci in a Rsc1-dependent manner. This activity can be transferred from Rsc1 to Rsc2 by swapping BAH domains. Secondly, RSC can aggregate nucleosomes into a large nuclease-resistant structure, termed an alphasome, in a Rsc2- and Rsc7-dependent manner. Thirdly, RSC positions nucleosomes at tRNA genes in a manner that requires both Rsc1 and Rsc2. Finally, chromatin particles consistent with previously described un-wound nucleosomes are confirmed to be present in specific promoter regions. Although Rsc1- and Rsc2- dependent subsets of these promoters could be identified, and associations with binding motifs for particular transcriptions factors were discovered, it was ultimately not possible to unambiguously define why some gene promoters depend on one RSC sub-unit rather than the other.