Abstract:
DNA topoisomerases are specialized nuclear enzymes that perform topological modifications on double stranded DNA and hence are essential for DNA metabolism such as replication, transcription, recombination, condensation and segregation. In a genetic screen we identified a temperature sensitive mutant allele of topoisomerase 2 that exhibit conditional synthetic lethality with a chk1 knockout strain. The mutant allele of topoisomerase 2 is defective in chromosome segregation at non permissive temperature and there was increase in chromosome segregation defects in double mutant of top2-10 and chk1 delete at non permissive temperature. More importantly topoisomearse 2 mutant cells mildly delay the mitotic progression at non permissive temperature that is mediated by checkpoint protein kinase Chk1. Additionally top2-10 mutant cells also activate the Chk1 at non permissive temperature and this activation of Chk1 takes place at the time of mitosis. Interestingly top2-10 mutant cells retain their viability at non permissive temperature if the cells are not allowed to enter into mitosis. Taken together our results, we speculate that in the top2-10 mutant, the segregation of entangled chromatids during mitosis could results in delaying the mitotic progression through the activation of Chk1 kinase.
