THE CDK7-CYCH-P36 COMPLEX OF TRANSCRIPTION FACTOR IIH PHOSPHORYLATES P53, ENHANCING ITS SEQUENCE-SPECIFIC DNA-BINDING ACTIVITY IN-VITRO

Phosphorylation is believed to be one of the mechanisms by which p53 b ecomes activated or stabilized in response to cellular stress. Previou sly, p53 was shown to interact with three components of transcription factor IIH (TFIIH): excision repair cross-complementing types 2 and 3 (ERCC2 and ERCC3) and p62. This communication demonstrates that p53 is phosphorylated by the TFIIH-associated kinase in vitro. The phosphory lation was found to be catalyzed by the highly purified kinase compone nts of TFIIH, the CDK7-cycH-p36 trimeric complex. The phosphorylation sites were mapped to the C-terminal amino acids located between residu es 311 and 393. Serines 371, 376, 378, and 392 may be the potential si tes for this kinase. Phosphorylation of p53 by this kinase complex enh anced the ability of p53 to bind to the sequence-specific p53-responsi ve DNA element as shown by gel mobility shift assays. These results su ggest that the CDK7-cycH-p36 trimeric complex of TFIIH may play a role in regulating p53 functions in cells.