The RAD51 protein supports homologous recombination by an exchange mechanism in mammalian cells

information concerning the function of recombination proteins in mammalian cells has been obtained from biochemical studies, but little is known about their mechanisms of action in growing cells. The eukaryotic recombination protein RAD51, a homologue of the Escherichia coli RecA protein, has been s hown to interact with various proteins, including the p53 protein, the guar dian of genomic stability maintenance. Here, the hamster RAD51 protein, CgR AD51, has been overexpressed in the SPD8 cell line, derived from Chinese ha mster V79 cells. This cell line offers unique possibilities for studying di fferent mechanisms for homologous recombination on endogenous substrates. W e report that the SPD8 cell line contains a mutated p53 gene, which provide s new insights into the recombination process in these cells. The present s tudy demonstrates that overexpression of CgRAD51 in these cells results in a two- to threefold increase in endogenous recombination. In addition, sequ ence analysis indicated that RAD51 promotes homologous recombination by a c hromatid exchange mechanism. (C) 1999 Academic Press.