THE ROLE OF DNA-REPAIR GENES IN RECOMBINATION BETWEEN REPEATED SEQUENCES IN YEAST

The presence of repeated sequences in the genome represents a potentia l source of karyotypic instability. Genetic control of recombination i s thus important to preserve the integrity of the genome. To investiga te the genetic control of recombination between repeated sequences, we have created a series of isogenic strains in which we could assess th e role of genes involved in DNA repair in two types of recombination: direct repeat recombination and ectopic gene conversion. Naturally occ urring (Ty elements) and artificially constructed repeats could be com pared in the same cell population. We have found that direct repeat re combination and gene conversion have different genetic requirements. T he role of the RAD51, RAD52, RAD54, RAD55, and RAD57 genes, which are involved in recombinational repair, was investigated. Based on the phe notypes of single and double mutants, these genes can be divided into three functional subgroups: one composed of RAD52, a second one compos ed of RAD51 and RAB54, and a third one that includes the RAD55 and RAD 57 genes. Among seven genes involved in excision repair tested, only R AD1 and RAD10 played a role in the types of recombination studied. We did not detect a differential effect of any rad mutation on Ty element s as compared to artificially constructed repeats.