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

Recently, we described a new biological function of p53 in inhibiting recombination processes when encountering mismatches in heteroduplexes (Dudenhöffer et al., 1998). Here, we characterized protein domains of p53 participating in this process by in vitro analysis of mutated p53 proteins, and by applying our SV40-based assay system on monkey cells, which express different p53 variants. We present evidence that both binding of artificial recombination intermediates and p53-dependent recombination control require an intact p53 core and the oligomerization domain, strongly suggesting that the recognition of DNA undergoing recombination represents an essential step of this genomic surveillance mechanism. Further analyses indicated a role of the C-terminus in negatively regulating recombination control, an effect which can be neutralized by concurrent mismatch recognition. p53 lacking the oligomerization domain totally lost its ability to suppress homologous recombination. The cancer-related mutant p53(273H) was also significantly defective in this function, although we observed only twofold reductions in the corresponding transactivation activities on p53-response elements in episomal constructs. HDM2, an inhibitor of p53's transcriptional and growth regulatory activities, interfered with the inhibition of DNA exchange processes by p53 only weakly. Thus, functions of p53 in recombination control can be structurally dissociated from p53-dependent transcriptional transactivation.