Fission yeast has three centromeres and their structure resembles that of metazoans. They are composed of a central domain that constitutes the kinetochore surrounded by outer repeats packaged in silent chromatin. Silent chromatin is characterized by underacetylated histone H3 and H4 and methylated histone H3 on lysine 9 by the SET-domain methyltransferase Clr4. These specific marks allow the binding of chromodomain proteins such as Swi6 and subsequent recruitment of cohesin. Non-coding transcripts have been detected from both strands of the outer repeats. The RNAi pathway processes these transcripts and the resulting siRNAs direct silent chromatin formation over these repeats causing transcriptional repression of an inserted marker gene. In order to find new components involved in the assembly of a functional kinetochore, the csp temperature sensitive mutants, previously shown to alleviate silencing of marker genes inserted at the outer repeats of centromere, were analyzed. Specifically components involved in RNA transcription and processing such as a subunit of RNA pol II (Csp3/Rpb7) and splicing factors (Csp4/Cwf10 and Csp5/Prp39) were required for the formation of silent chromatin by affecting the production of centromeric transcripts. Fission yeast silent chromatin formation is dependent on methylation of histone H3 on lysine 9. In order to identify additional factors that might directly affect modification of histones tails, four genes encoding for SET domain protein which may represent putative histone methyltransferase were deleted (<i>set3, set6, set7</i> and <i>set9</i>). No affect on silent chromatin formation was detected. In a collaborative study Set9 was found to specifically methylate lysine 20 on histone H4 and to be involved in the general genome integrity. Methylation on lysine 20 of histone H4 together with phosphorylation of serine 129 of histone 1-12A is necessary to maintain the DNA damage checkpoint activity through the recruitment of Cbr2 at the sites of DNA damage.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:660701 |
| Date | January 2005 |
| Creators | Portoso, Manuela |
| Publisher | University of Edinburgh |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/1842/12129 |
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