Efficient incorporation of large (> 2 kb) heterologies into heteroduplex DNA: Pms1/Msh2-dependent and -independent large loop mismatch repair in Saccharomyces cerevisiae

DNA double-strand break (DSB) repair in yeast is effected primarily by gene conversion. Conversion call conceivably result from gap repair or from mis match repair of heteroduplex DNA (hDNA) in recombination intermediates. Mis match repair is normally very efficient, but unrepaired mismatches segregat e in the next cell division, producing sectored colonies. Conversion of sma ll heterologies (single-base differences or insertions < 15 bp) in meiosis and mitosis involves mismatch repair of hDNA. The repair of larger loop mis matches in plasmid substrates or arising by replication slippage is ineffic ient and/or independent of Pms1p/Msh2p-dependent mismatch repair. However, large insertions convert readily (without sectoring) during meiotic recombi nation, raising the question of whether large insertions convert by repair of large loop mismatches or by gap repair. Wt show that insertions of 2.2 a nd 2.6 l;bp convert efficiently during DSB-induced mitotic recombination, p rimarily: by Msh2p- and Pms1p-dependent repair of large loop mismatches. Th ese results support models in which Rad51p readily incorporates large heter ologies into hDNA. We also show that large heterologies convert more freque ntly than small heterologies located the same distance from an initiating D SB and propose that this reflects Msh2-independent large loop-specific mism atch repair biased toward loop loss.