Holliday junction cleavage by yeast Rad1 protein

IN Saccharomyces cerevisiae, of the many genes required for excision repair of ultraviolet-damaged DNA, only RAD1 and RAD10 also function in genetic recombination¹. Complex formation between the RAD1 and RAD10 gene products¹ activates an endo-nucleolytic function that nicks single-stranded DNA^2,3 and negatively supercoiled double-stranded DNA². To characterize the recombination role of the proteins Radl and Radl0, we have investigated their interaction with the Holliday junction, a four-stranded structure that results from single-stranded crossover between two duplex DNA molecules and whose resolution is obligatory for the generation of mature recombinants. We show that Radl binds specifically to a Holliday junction and, in the presence of magnesium, catalyses the endonucleolytic cleavage of the junction. Junction cleavage by Radl proceeds sufficiently without Radl0, thus identifying Radl as the catalytic subunit of Radl/Radl0 endonuclease.