LAUSR

Mus81 is a well‐conserved DNA structure‐specific endonuclease which belongs to the XPF/Rad1 family of proteins that are involved in DNA nucleotide excision repair. Mus81 forms a heterodimer with a non‐catalytic subunit, Mms4, in Saccharomyces cerevisiae (Eme1/EME1 in Schizosaccharomyces pombe and mammals). Recent evidence shows that Mus81 functions redundantly with Sgs1, a member of the ubiquitous RecQ family of DNA helicases, to process toxic recombinant intermediates. In budding yeast, homologous recombination is regulated by the Rad52 epistasis group of proteins, including Rad52, which stimulates the main steps of DNA sequence‐homology searching. Mus81 was proven to act in the Rad52‐dependent pathway. Here, we demonstrate that Rad52 and Mus81–Mms4 possesses a functional interaction; the presence of Rad52 significantly enhances the endonuclease activity of Mus81–Mms4 on a broad range of its preferred synthetic substrates. Furthermore, this functional interaction is demonstrated to be species specific. We fragmented Rad52 and found that the N‐terminal fragment from the 86th to 169th amino acid residue, which belongs to DNA‐binding and self‐association domains, can stimulate Mus81–Mms4 endonuclease. These results strongly support the notion that Rad52 and Mus81–Mms4 collaborate and work jointly in processing of homologous recombination intermediates.