Isolation and characterization of the RAD59 homologue of Kluyveromyces lactis

Homologous recombination in the yeast Saccharomyces cerevisiae is under the control of the RAD52 epistasis group. Genes belonging to this group show s trong conservation during evolution and homologues of most members have bee n identified in other eukaryotic organisms such as Schizosaccharomyces pomb e, Drosophila and mammals. A homologue of the ScRAD59 gene, which shows str uctural and functional overlap with ScRAD52, has not been identified in oth er organisms until now. Previous assessment of the ScRAD59 function reveale d that the product of this gene is required for certain types of ScRAD51-in dependent recombination and single-strand annealing. Also, in the distantly related fission yeast, Sch. pombe, a second RAD52 homologue has been ident ified (rad22B(+)), but this gene more closely resembles ScRAD52 than ScRAD5 9 at the amino-acid level. In this study, the isolation of a homologue of S cRAD59 in Kluyveromyces lactis, KlRAD59, is described. A Klrad59 null allel e results in moderate sensitivity to X-rays, indicating that the KlRAD59 ge ne is involved in the repair of X-ray-induced DNA damage. The amino acids i n the putative KlRad59 protein share 53% identity and 11% similarity with S cRad59. The KlRAD59 gene fully complements both the X-ray-sensitive phenoty pe and defects in recombination of the Scrad59 mutant strain. Our results u nderscore the evolutionary conservation of the RAD52 group of genes and pro vide evidence that the presence of additional RAD52 homologues is not limit ed to Sac. cerevisiae and Sch. pombe and might be a general phenomenon.