The activation of replication origins is temporally regulated in S phase, with some origins activating early and some late. The molecular events controlling the temporal programme are not well understood, but in S. cerevisiae there is a close relationship between telomere length and nearby origin activation time. In the first part of this thesis I explore how the initiation time of origins near to telomeres is regulated by telomere length in a manner dependent on the Tel1 kinase. I demonstrate that an induced short telomere drives early activation of a nearby origin, but that in the absence of Tel1 the same origin activates late. In the second, major part of this thesis I focus on how the Rif1 protein negatively regulates length of the terminal TG1-3 repeats. While Rif1 has long been known to control telomere length, the mechanism through which Rif1 prevents telomere over-extension has remained unclear. Recently Rif1 was discovered to act in DNA replication control as a Protein Phosphatase 1-targeting subunit, directing Protein Phosphatase 1 (PP1) to dephosphorylate the MCM replicative helicase complex. I therefore investigated whether Rif1 also controls telomere length through PP1 interaction. I examine the effects of a mutant Rif1 with its PP1 interaction sites mutated to ablate PP1 binding. I found the mutant Rif1 binds normally to telomeres but causes a long telomere phenotype, similar to that in ∆rif1 cells, implicating Rif1-PP1 interaction in telomere length control. In further experiments I show that tethered PP1 can partially substitute for Rif1 in telomere length control. I also establish that the effect of Rif1-PP1 on telomere length does not operate indirectly through replication timing control, but rather appears to act through a direct pathway controlling telomerase recruitment. I discuss potential dephosphorylation targets, and the mechanism through which Rif1 and PP1 may control telomere length homeostasis. To summarise, my PhD research demonstrates that S. cerevisiae Rif1 acts with PP1 to repress telomerase-mediated TG1-3 repeat extension.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:737941 |
| Date | January 2017 |
| Creators | Kedziora, Sylwia Maria |
| Publisher | University of Aberdeen |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?pid=235993 |
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