MISMATCH REPAIR OF HETERODUPLEX DNA INTERMEDIATES OF EXTRACHROMOSOMALRECOMBINATION IN MAMMALIAN-CELLS

Previous work indicated that extrachromosomal recombination in mammali an cells could be explained by the single-strand annealing (SSA) model . This model predicts that extrachromosomal recombination leads to non conservative crossover products and that heteroduplex DNA (hDNA) is fo rmed by annealing of complementary single strands. Mismatched bases in hDNA may subsequently be repaired to wild-type or mutant sequences, o r they may remain unrepaired and segregate following DNA replication. We describe a system to examine the formation and mismatch repair of h DNA in recombination intermediates. Our results are consistent with ex trachromosomal recombination occurring via SSA and producing crossover recombinant products. As predicted by the SSA model, hDNA was present in double-strand break-induced recombination intermediates. By placin g either silent or frameshift mutations in the predicted hDNA region, we have shown that mismatches are efficiently repaired prior to DNA re plication.