P53 BINDS SINGLE-STRANDED-DNA ENDS THROUGH THE C-TERMINAL DOMAIN AND INTERNAL DNA SEGMENTS VIA THE MIDDLE DOMAIN

We have previously reported that wild-type p53 can bind single-strande d (ss) DNA ends and catalyze renaturation of ss complementary DNA mole cules. Here we demonstrate that p53 can also bind to internal segments of ss DNA molecules via a binding site (internal DNA site) distinct f rom the binding site for DNA ends (DNA end site). Using p53 deletion m utants, the internal DNA site was mapped to the central region (residu es 99-307), while the DNA end site was mapped to the C-terminal domain (residues 320-393) of the p53 protein. The internal DNA site can be a ctivated by the binding of ss DNA ends to the DNA end site. The C-term inal domain alone was sufficient to catalyze DNA renaturation, althoug h the central domain was also involved in promotion of renaturation by the full-length protein. Our results suggest that the interaction of the C-terminal tail of p53 with ss DNA ends generated by DNA damage in vivo may lead to activation of non-specific ss DNA binding by the cen tral domain of p53.