Biochemical characterization of the RNA-binding and RNA–DNA strand exchange activities of the human RAD52 protein

RAD52 is a single-stranded DNA (ssDNA) binding protein that functions in the repair of DNA double-strand breaks (DSBs) by promoting the annealing of complementary DNA strands. RAD52 may also play an important role in an RNA transcript-dependent type of DSB repair, in which it reportedly binds to RNA and mediates the RNA–DNA strand exchange reaction. However, the mechanistic details of these functions are still unclear. In the present study, we utilized the domain fragments of RAD52 to biochemically characterize the single-stranded RNA (ssRNA) binding and RNA–DNA strand exchange activities of RAD52. We found that the N-terminal half of RAD52 is primarily responsible for both activities. By contrast, significant differences were observed for the roles of the C-terminal half in RNA–DNA and DNA–DNA strand exchange reactions. The C-terminal fragment stimulated the inverse RNA–DNA strand exchange activity displayed by the N-terminal fragment in trans, whereas the trans stimulatory effect by the C-terminal fragment was not observed in the inverse DNA–DNA or forward RNA–DNA strand exchange reactions. These results suggest the specific function of the C-terminal half of RAD52 in RNA-templated DSB repair.