P53-MEDIATED DNA RENATURATION CAN MIMIC STRAND EXCHANGE

The process of strand exchange is considered to be the hallmark of DNA recombination. Proteins known to carry out such exchange are believed to operate via one or the other of two mechanisms, RecA-like proteins promote the formation of a three-stranded or tripler synaptic interme diate in which strand exchange occurs, whereas other proteins would al low the coordinated exonucleolytic degradation of one strand in the du plex DNA and its replacement by an invading strand of similar sequence and polarity, In view of properties ascribed to it, we have attempted to determine whether p53 belongs to one or the other of these groups of proteins. The in vitro assay used relies on a double-stranded (ds) oligonucleotide (oligo 1+2) and a single-stranded (ss) oligonucleotide (oligo 3), part of which is complementary to oligo 1. The data collec ted suggest that, under the conditions of the assay, oligo 1+2 undergo es partial denaturation; p53 then catalyzes renaturation of oligo 1 wi th oligo 3, rather than true strand exchange, Since p53 is not known f or being able to 'melt' DNA, it would seem unlikely that this protein would effect strand exchange in vivo without assistance from another, denaturing, protein.