Specificity of cyclin E-Cdk2, TFIIB, and E1A interactions with a common domain of the p300 coactivator

The p300 and CREB binding protein (CBP) transcriptional coactivators intera ct with a variety of transcription factors and regulate their activity. Amo ng the interactions that have been described, the COOH-terminal region of p 300 binds to cyclin E-cyclin-dependent kinase 2 (cyclin E-Cdk2) and TFIIB, as well as to the EIA gene products of adenovirus. Inhibition of Cdk activi ty by Cdk inhibitors, such as p21 or p27, potentiates NF-KB activity and pr ovides a mechanism to coordinate cell cycle progression with the transcript ion of genes expressed during growth arrest. In this report, we analyze the specific domains of p300 required for the binding of p300 to cyclin E-Cdk2 , TFIIB, and E1A and the ability of these proteins to interact with p300, a lone or in combination. 12S E1A, an inhibitor of p300-dependent transcripti on, reduces the binding of TFIIB, but not that of cyclin E-Cdk2, to p300. I n contrast, 13S E1A, a pleiotropic transcriptional activator, does not inhi bit TFIIB binding to p300, although it enhances the interaction of cyclin E -Cdk2,vith p300. Modification of cyclin E-Cdk2 is most likely required for association with p300 since the interaction is observed only with cyclin E- Cdk2 purified from mammalian cells. Domain swap studies show that the cycli n homology domain of TFIIB is involved in interactions with p300, although the homologous region from cyclin E does not mediate this interaction. Thes e findings suggest that p300 or CBP function is regulated by interactions o f various proteins with a common coactivator domain.