Repair of DNA loops involves DNA-mismatch and nucleotide-excision repair proteins

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Abstract
A number of enzymes recognize and repair DNA lesions1. The DNA-mismatch repair system corrects base–base mismatches andsmall loops, whereas the nucleotide-excision repair systemremoves pyrimidine dimers and other helix-distorting lesions. DNA molecules with mismatches or loops can arise as aconsequence of heteroduplex formation during meiotic recombination2. In the yeast Saccharomyces cerevisiae, repair of mismatches results in gene conversion or restoration, and failure to repair the mismatch results in post-meiotic segregation (PMS) (Fig. 1). The ratio of gene-conversion to PMS events reflects the efficiency of DNA repair3,4. By examining the PMS patterns in yeast strains heterozygous for a mutant allele with a 26-base-pair insertion, we find that the repair of 26-base loops involves Msh2 (a DNA-mismatch repair protein) and Rad1 (a protein required for nucleotide-excision repair).