INVOLVEMENT OF THE PS03 GENE OF SACCHAROMYCES-CEREVISIAE IN INTRACHROMOSONAL MITOTIC RECOMBINATION AND GENE AMPLIFICATION

Using a genetic system of haploid strains of Saccharomyces cerevisiae carrying a duplication of the his4 region on chromosome III, the pso3- 1 mutation was shown to decrease the rate of spontaneous mitotic intra chromosomal recombination 2- to 13-fold. As previously found for the r ad52-1 mutant, the pso3-1 mutant is specifically affected in mitotic g ene conversion. Moreover, both mutations reduce the frequency of spont aneous recombination. However, the two mutations differ in the extent to which they affect recombination between either proximally or distal ly located markers on the two his4 heteroalleles. In addition, amplifi cations of the his4 region were detected in the pso3-1 mutant. We sugg est that the appearance of these amplifications is a consequence of th e inability of the pso3-1 mutant to perform mitotic gene conversion.