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Title: Rif1 regulates the fate of telomere entanglements during M-phase
Author: Zaaijer, S.
ISNI:       0000 0004 5363 746X
Awarding Body: University College London (University of London)
Current Institution: University College London (University of London)
Date of Award: 2014
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The protection of chromosome ends, and in turn genome stability, is intimately linked with the ability of telomeres to replicate and segregate with high fidelity. It has been shown previously that Taz1, the fission yeast ortholog of mammalian TRF1 and TRF2, is critical for promoting passage of the replication fork through telomere sequences. Deletion of taz1+ results in stalled telomeric replication forks that fail to resume. These defective replication intermediates lead to telomere entanglements that fail to be resolved in mitosis at cold temperatures, leading taz1Δ cells to be cold sensitive. It is not yet known exactly what entanglements are, why they occur at cold temperatures, and how (or if) they are resolved. In this thesis telomere entanglements are further investigated. We found that in taz1∆ cells grown in the cold, entangled telomeres can be visualized as DNA masses persisting between separating sister chromatids during M-phase. We have observed sister chromatid masses which remain connected either by histone bound DNA resulting in aberrant chromosome segregation morphologies, or by ssDNA coated with Rad11RPA and Rad22Rad52. The former was observed to be highly dangerous, the latter can be processed and cells can continue to the next cell cycle. Rif1, a conserved replication/repair protein sparked our interest when we observed that rif1+ deletion suppresses taz1Δ cold sensitivity. However, the function of Rif1 was a mystery; revealing the role of Rif1 in cells lacking taz1+ formed the next part of this thesis. We have found that Rif1 acts in removal of telomeric entanglements rather than at the fork-stalling events that generate them. Although Rif1 is reported to bind telomeres in a Taz1-dependent manner, we observe Rif1 at the mid-zone during anaphase in wild type and taz1∆ cells, associated to thin DNA stretches. Artificially recruiting Rif1 to a taz1∆ telomere is lethal in the cold, indicating that the departure of Rif1 from the telomere is essential for viability and presumably for entanglement resolution. We propose a newly identified role for Rif1 in regulating the resolution of entangled DNA during M-phase.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available