Isolation and characterization of the RAD59 homologue of Kluyveromyces lactis

Abstract.

Homologous recombination in the yeast Saccharomyces cerevisiae is under the control of the RAD52 epistasis group. Genes belonging to this group show strong conservation during evolution and homologues of most members have been identified in other eukaryotic organisms such as Schizosaccharomyces pombe, Drosophila and mammals. A homologue of the ScRAD59 gene, which shows structural and functional overlap with ScRAD52, has not been identified in other organisms until now. Previous assessment of the ScRAD59 function revealed that the product of this gene is required for certain types of ScRAD51-independent recombination and single-strand annealing. Also, in the distantly related fission yeast, Sch. pombe, a second RAD52 homologue has been identified (rad22B ⁺), but this gene more closely resembles ScRAD52 than ScRAD59 at the amino-acid level. In this study, the isolation of a homologue of ScRAD59 in Kluyveromyces lactis, KlRAD59, is described. A Klrad59 null allele results in moderate sensitivity to X-rays, indicating that the KlRAD59 gene is involved in the repair of X-ray-induced DNA damage. The amino acids in the putative KlRad59 protein share 53% identity and 11% similarity with ScRad59. The KlRAD59 gene fully complements both the X-ray-sensitive phenotype and defects in recombination of the Scrad59 mutant strain. Our results underscore the evolutionary conservation of the RAD52 group of genes and provide evidence that the presence of additional RAD52 homologues is not limited to Sac. cerevisiae and Sch. pombe and might be a general phenomenon.