The budding yeast Mei5–Sae3 complex interacts with Rad51 and preferentially binds a DNA fork structure

Abstract

Meiotic homologous recombination in Saccharomyces cerevisiae involves formation of nucleoprotein filaments of Rad51 and Dmc1 that mediate DNA strand exchange between homologous chromosomes. The Mei5–Sae3 protein complex functions as a recombination mediator to promote nucleation of the Dmc1 recombinase onto replication protein A-coated single-stranded DNA. Here, we have expressed and purified the Mei5 protein, Sae3 protein and the Mei5–Sae3 complex for biochemical studies. We show the Mei5–Sae3 complex preferentially binds a fork-like DNA substrate to 3′ overhanging DNA, single-stranded DNA or double-stranded DNA. We demonstrate that Mei5 confers DNA binding activity to the Mei5–Sae3 complex. We determined Mei5–Sae3 interacts with the Rad51 recombinase through the N-terminal domain of Mei5. Unlike Rad52, Mei5–Sae3 lacks recombination mediator activity for Rad51. Importantly, we find that the Mei5–Sae3 complex does not harbor single-strand DNA annealing activity. These properties of the Mei5–Sae3 complex distinguishes it from the Rad52 protein, which serves as the mediator of Rad51 and is involved in the single-strand DNA annealing pathway of homologous recombination.