Analysis of the indispensable RAD51 cofactor BRCA2 in , a Basidiomycota yeast.

The tumor suppressor plays a critical role in homologous recombination by regulating RAD51, the eukaryotic homologous recombinase. We identified the BRCA2 homolog in a Basidiomycota yeast, BRCA2 homologs are found in many Basidiomycota species but not in Ascomycota species. BRCA2 (Brh2, for CA2 omolog) is about one-third the size of human BRCA2. Brh2 carries three potential BRC repeats with two oligonucleotide/oligosaccharide-binding domains. The homolog of DSS1, a small acidic protein serving as an essential partner of BRCA2 was also identified. The yeast two-hybrid assay shows the interaction of Brh2 with both Rad51 and Dss1. Unlike human BRCA2, Brh2 is not required for normal cell growth, whereas loss of Dss1 results in slow growth. The loss of Brh2 caused pronounced sensitivity to UV and ionizing radiation, and their HR ability, as assayed by gene-targeting efficiency, is compromised. These phenotypes are indistinguishable from those of the mutant, and the double mutant. Brh2 is likely the BRCA2 ortholog that functions as an indispensable auxiliary factor for Rad51.