Dissection of the sequence-specific DNA binding and exonuclease activities reveals a superactive yet apoptotically impaired mutant p53 protein

Both sequence-specific DNA binding and exonuclease activities have been mapped to the central conserved core domain of p53.  To gain more information about these two activities a series of mutants were generated that changed core domain histidine residues.  Of these mutants, only one, H115N p53, showed markedly reduced exonuclease activity (ca. 15% of wild-type). Surprisingly, purified H115N p53 protein was found to be significantly more potent than wild-type p53 in binding to DNA by several criteria including gel mobility shift assay, filter binding and DNase I footprinting.  Interestingly as well, non-specific DNA binding by the core domain of H115N p53 is superior to that of wild-type p53.  To study H115N p53 in vivo, clones of H1299 cells expressing tetracycline regulated wild-type or H115N p53 were generated.  H115N was both more potent than wild-type p53 in inducing p53 target genes such as p21 and PIG3 and was also more effective in arresting cells in G1.  Unexpectedly, in contrast to wild-type p53...