Overlapping roles for PSO2 and MSH2-EXO1 in DNA repair.
Peter J. McHugh (1), Louise J. Barber (2), John A. Hartley (1), Thomas A. Ward (1)
(1) Cancer Research UK, WIMM, University of Oxford, Oxford, OX3 9DS, UK;
(2) Dept. Oncology, UCL Medical School, London W1W 7BS, UK
Yeast pso2 mutants are specifically sensitive to agents that induce DNA interstrand cross-links (ICLs), including many antitumour drugs. We have discovered an overlapping function for PSO2 with the mismatch repair factor MSH2 and its associated 5'-3' exonuclease EXO1 in the repair of DNA interstrand cross-links. Exponentially growing cells doubly disrupted for pso2 and msh2 show a synergistic increase in sensitivity to cross-linking agents and an absolute defect in the repair of the double-strand breaks induced by these drugs. The overlapping role of PSO2 and MSH2 extends to DNA double-strand break repair more generally, since pso2 msh2/exo1 double disruptants mutants demonstrate enhanced sensitivity to ionising radiation. Using a chromosomally integrated inverted repeat substrate, we found that loss of both PSO2 and EXO1/MSH2 also affects spontaneous homologous recombination with rates reduced to levels similar to those observed in a rad51 strain with this construct. Physical analysis of the recombination outcomes indicates that both gene conversions and crossovers are equally reduced in pso2 exo1 cells, suggesting an early role for Pso2 and Msh2-Exo1 in the processing of spontaneous and induced DNA lesions that are channelled into homologous recombination.
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