RAD51 supports spontaneous non-homologous recombination in mammalian cells, but not the corresponding process induced by topoisomerase inhibitors

The RAD51 protein has been shown to participate in homologous recombination by promoting ATP-dependent homologous pairing and strand transfer reaction s. In the present study, we have investigated the possible involvement of R AD51 in non-homologous recombination, We demonstrate that overexpression of CgRAD51 enhances the frequency of spontaneous non-homologous recombination in the hprt gene of Chinese hamster cells. However, the rate of non-homolo gous recombination induced by the topoisomerase inhibitors campothecin and etoposide was not altered by overexpression of RAD51. These results indicat e that the RAD51 protein may perform a function in connection with spontane ous non-homologous recombination that is not essential to or not rate-limit ing for non-homologous recombination induced by camptothecin or etoposide, We discuss the possibility that the role played by RAD51 in non-homologous recombination observed here may not be linked to non-homologous end-joining .