Isolation and Characterization of Point Mutations in Mismatch Repair Genes That Destabilize Microsatellites in Yeast

Abstract

The stability of simple repetitive DNA sequences (microsatellites) is a sensitive indicator of the ability of a cell to repair DNA mismatches. In a genetic screen for yeast mutants with elevated microsatellite instability, we identified strains containing point mutations in the yeast mismatch repair genes, MSH2, MSH3, MLH1, and PMS1. Some of these mutations conferred phenotypes significantly different from those of null mutations in these genes. One semidominant MSH2mutation was identified. Finally we showed that strains heterozygous for null mutations of mismatch repair genes in diploid strains in yeast confer subtle defects in the repair of small DNA loops.

ACKNOWLEDGMENTS

The research was supported by a National Institutes of Health Grant, GM52319 (T.D.P.). E.A.S. is a recipient of a Burroughs Wellcome Fund Career Award in the Biomedical Sciences.

We thank R. M. Liskay and E. Alani for comments on the manuscript. We also thank E. Alani for generously supplying the anti-Msh2p antibody.