DNA topoisomerase 2 mutant allele mildly delays the mitotic progression and activates the checkpoint protein kinase Chk1 in fission yeast

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.