DNA-binding domain within the Brh2 N terminus is the primary interaction site for association with DNA

Abstract

The C-terminal region of Brh2 (Brh2CT), the BRCA2 homolog in Ustilago maydis, is highly conserved and aligns with the DSS1/ DNA-binding domain (DBD) of mammalian BRCA2, while the N-terminal region (Brh2NT) is poorly conserved and has no obvious functional domain except for the single Rad51-interacting BRC element. Paradoxically, Brh2NT, but not Brh2CT, complements the DNA repair and recombination deficiency of the brh2 mutant. We show here that Brh2NT exhibits an unexpected DNA binding activity with properties similar to that of the full-length protein. Deletion mapping localized the region responsible for the DNA binding activity to a stretch of residues between the BRC element and the canonical DBD. A heterologous DNA-binding domain from the large subunit of replication protein A substituted for the endogenous binding region within Brh2NT in supporting DNA repair. Rad51-promoted strand invasion was stimulated by Brh2NT, but required the presence of the BRC element. The findings suggest a model in which Brh2NT serves as the principal site for association with DNA, while the Brh2CT provides a means for regulation. © 2009 by The American Society for Biochemistry and Molecular Biology, Inc.