THE DOMAIN OF P53 REQUIRED FOR BINDING HPV-16 E6 IS SEPARABLE FROM THE DEGRADATION DOMAIN

The E6 proteins of specific cancer-associated human papillomaviruses ( HPVs) complex with and mediate degradation of the cellular anti-oncoge ne p53 in vitro. A critical property of p53 is its ability to stimulat e transcription from promoters containing its recognition sequence. HP V E6, mutant p53 proteins, and several DNA tumor virus oncogenes inhib it the transcriptional activity of wild-type p53. In this report, the structural requirements for the interaction between HPV 16 E6 and p53 were examined both in vivo and in vitro. p53-stimulated transcription was efficiently inhibited by wild-type HPV 16 E6 and E6 mutants compet ent for p53 binding and degradation. A series of p53 deletions and hyb rid proteins with heterologous DNA binding, dimerization and transacti vation domains were analysed for transcriptional interaction with HPV 16 E6 to determine the domains of p53 required for transcriptional inh ibition. These chimeric proteins were also analysed for E6 binding and E6-mediated degradation in vitro. In both assays, complex formation w ith E6 was mediated through the amino-terminal 345 amino acids of p53 without a specific requirement for its C-terminus. Hybrid proteins con taining residues 161-345 of p53 also bound E6, but this segment of p53 was not susceptible to E6 induced proteolysis. A second region of p53 , within its N-terminal 160 aa, is required for E6 induced degradation of complexed p53. Taken together, these results suggest that the comp lex formation between E6 and p53 is not mediated through the C-terminu s of p53 and that binding and degradation are separable.