Dissociation of the recombination control and the sequence-specific transactivation function of P53

Recently, we described a new biological function of p53 in inhibiting recom bination processes when encountering mismatches in heteroduplexes (Dudenhof fer et al,, 1998). Here, we characterized protein domains of p53 participat ing in this process by in vitro analysis of mutated p53 proteins, and by ap plying our SV40-based assay system on monkey cells, which express different p53 variants. We present evidence that both binding of artificial recombin ation intermediates and p53-dependent recombination control require an inta ct p53 core and the oligomerization domain, strongly suggesting that the re cognition of DNA undergoing recombination represents an essential step of t his genomic surveillance mechanism, Further analyses indicated a role of th e C-terminus in negatively regulating recombination control, an effect whic h can be neutralized by concurrent mismatch recognition. p53 lacking the ol igomerization domain totally lost its ability to suppress homologous recomb ination. The cancer-related mutant p53(273H) was also significantly defecti ve in this function, although we observed only twofold reductions in the co rresponding transactivation activities on p53-response elements in episomal constructs. HDM2, an inhibitor of p53's transcriptional and growth regulat ory activities, interfered with the inhibition of DNA exchange processes by p53 only weakly, Thus, functions of p53 in recombination control can be st ructurally dissociated from p53-dependent transcriptional transactivation.