Structural and kinetic analysis of p53-DNA complexes and comparison of human and murine p53.

Sequence-specific DNA binding by p53 is dependent upon protein conformation. The 1620+ form correlates with wild type p53 suppressor function and is a prerequisite for binding to the DNA consensus p53-CON in vitro. It has been reported that murine p53 changes conformation on interaction with high affinity DNA target sequences and in the present study we have analysed p53-DNA complexes using conformation-specific monoclonal antibodies against p53. For murine p53 (mp53) we show (i) the 1620+ form is retained and stabilised in complex with DNA, and (ii) the complexes are dissociated by the PAb1620 monoclonal antibody. In contrast, PAb1620 did not detect nor dissociate human p53-DNA complexes nor did it interfere with complex formation. In competition experiments murine p53 replaced human p53 (hp53) in p53-DNA complexes and this correlated with the greater lability observed for hp53-DNA complexes at a given temperature. Mixed human-murine p53 oligomers were competent for DNA binding with an estimated affinity around 5 x 10(-10) M, similar to that observed for either human or murine p53 alone. The potential significance of these observations is discussed in relation p53 function in vivo.