title: Mutator phenotype due to loss of heterozygosity in diploid yeast strains with mutations in MSH2 and MLH1.
abstract: Mutations in mismatch repair (MMR) genes predispose humans to cancer. Particularly prevalent are frameshift and point mutations in MSH2 and MLH1, two genes whose products are required for the early steps in MMR. In normal tissues of persons predisposed to hereditary non-polyposis colon cancer (HNPCC), these mutations are usually present in only one allele. In tumor cells of these patients, the second, wild type allele is typically found to be deleted or inactivated by point mutation. This suggests that loss of heterozygosity (LOH) results in a strong mutator phenotype that could eventually lead to the onset of disease. Here we demonstrate that diploid yeast strains that are heterozygous for MSH2 and MLH1 alleles have an elevated mutation rate. We further show that this effect results not from saturation of the MMR capacity of all cells in the population, but rather from loss of the wild type allele in a subpopulation of heterozygous cells. These results have implications for understanding the mechanisms of carcinogenesis in humans.
authors.affiliation: Laboratory of Molecular Genetics, National Institute of Environmental Health Sciences, Research Triangle Park, NC, USA.
authors.forename: K
authors.initials: K
authors.lastname: Drotschmann
authors.forename: P V
authors.initials: PV
authors.lastname: Shcherbakova
authors.forename: T A
authors.initials: TA
authors.lastname: Kunkel
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D020137:Base Pair Mismatch / Q000235:genetics*; D002352:Carrier Proteins; D003110:Colonic Neoplasms / Q000235:genetics; D004260:DNA Repair / Q000235:genetics; D004268:DNA-Binding Proteins / Q000235:genetics*; D004171:Diploidy; D005656:Fungal Proteins / Q000235:genetics*; D006579:Heterozygote; D006801:Humans; D019656:Loss of Heterozygosity; D000070957:MutL Protein Homolog 1; D051718:MutS Homolog 2 Protein; D009363:Neoplasm Proteins / Q000235:genetics*; D009687:Nuclear Proteins; D010641:Phenotype; D017354:Point Mutation; D015003:Yeasts / Q000235:genetics*
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D002352:Carrier Proteins; D004268:DNA-Binding Proteins; D005656:Fungal Proteins; C501486:MLH1 protein, human; D009363:Neoplasm Proteins; D009687:Nuclear Proteins; D000070957:MutL Protein Homolog 1; D051718:MutS Homolog 2 Protein