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Title: Investigation into the regulation of DNA repair by the S. pombe cell cycle kinase Cdc2-cyclinB
Author: Ewert-Krzemieniewska, Katarzyna
ISNI:       0000 0004 2681 1477
Awarding Body: Prifysgol Bangor University
Current Institution: Bangor University
Date of Award: 2009
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The work presented in this thesis proposes two novel functions for S. pombe Cdc2 in the cell cycle-dependent coordination of DNA recombination: (i) during unperturbed cell cycle and (ii) in response to camptothecin (CPT)-induced DNA breaks. In unperturbed cells, in vivo elevated Cdc2 activity causes problems during DNA replication that lead to an increase in spontaneous gene conversion between sister chromatids and enhanced loss of a non-essential minichromosome. Data presented here suggest that Cdc2 regulates the anti-recombinogenic activity of the Srs2 DNA helicase to prevent such spontaneous gene conversion events in S phase. Both proteins associate with PCNA in distinct protein complexes, which may allow them to regulate DNA repair in S phase. Elevated Cdc2 activity leads to constitutive phosphorylation of the checkpoint kinase Chk1, indicating that the inability to regulate Srs2 DNA helicase causes DNA replication lesions, which engage the G2-M checkpoint. Cells with elevated Cdc2 activity are specifically sensitive to the Topoisomerase I (Top1) poison CPT. The camptothecin sensitivity of cdc2.1w mutant cells increases in the absence of Tyrosyl-DNA-phosphodiesterase (Tdp1), which cleaves immobilised Top1 releasing it from the 3'-end of DNA in S phase. As during the unperturbed cell cycle, Cdc2 appears to regulate Srs2 DNA helicase under these circumstances. Srs2 may unwind the blocked 3'-strand in the absence of Tdp1 to allow a nuclease to access the damaged site. Both Mus81 and Rad16 are potential candidates since both nucleases act in the Cdc2-dependent pathway in response to CPT. Although all "wee" mutants with elevated Cdc2 activity are defective in this CPT repair pathway, both Wee1 and Mik1 kinase may perform independent repair functions.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available