HOMOLOGOUS AND HOMEOLOGOUS INTERMOLECULAR GENE CONVERSION ARE NOT DIFFERENTIALLY AFFECTED BY MUTATIONS IN THE DNA-DAMAGE OR THE MISMATCH REPAIR GENES RAD1, RAD50, RAD51, RAD52, RAD54, PMS1 AND MSH2

Mismatch repair (MMR) genes or genes involved in both DNA damage repai r and homologous recombination might affect homeologous vs. homologous recombination differentially. Spontaneous mitotic gene conversion bet ween a chromosome and a homologous or homeologous donor sequence (14% diverged) on a single copy plasmid was examined in wild-type Saccharom yces cerevisiae strains and in MMR or DNA damage repair mutants. Homol ogous recombination in rad51, rad52 and rad54 mutants was considerably reduced, while there was little effect of rad1, rad50, pms1 and msh2 null mutations. DNA divergence resulted in no differential effect on r ecombination rates in the wild type or the mutants; there was only a f ive- to 10-fold reduction in homeologous relative to homologous recomb ination regardless of background. Since DNA divergence is known to aff ect recombination in some systems, we propose that differences in the role of MMR depends on the mode of recombination and/or the level of d ivergence. Based on analysis of the recombination breakpoints, there i s a minimum of three homologous bases required at a recombination junc tion. A comparison of Rad(+) vs. rad52 strains revealed that while all conversion tracts are continuous, elimination of RAD52 leads to the a ppearance of a novel class of very short conversion tracts.