CHARACTERIZATION OF MONOCLONAL-ANTIBODIES RAISED AGAINST P300 - BOTH P300 AND CBP ARE PRESENT IN INTRACELLULAR TBP COMPLEXES

The amino terminus of the adenovirus E14 protein is involved in E14 tr ansforming functions, repression of tissue-specific gene expression, a nd E1A-mediated enhancer repression, These N-terminal functions are as sociated with the ability of this region of E1A to bind to p300 and CB P, two closely related cellular proteins thought to function as transc riptional adaptor molecules. Here we describe the characterization of a panel of 11 monoclonal antibodies raised against E1A-affinity-purifi ed 300-kDa proteins. The panel can be divided into two groups based on immunoprecipitation patterns, The first group consists of five p300/C BP-cross-reactive and two p300-specific monoclonal antibodies, all of which immunoprecipitate p300 and/or CBP without associated cellular pr oteins. In contrast, the second group immunoprecipitates p300 or both p300 and CBP in association with a complex of at least seven other cel lular proteins, Taking advantage of the specificities of these monoclo nal antibodies, we have identified both p300 and CBP in in vivo comple xes with TBP, a finding consistent with a role for both p300 and CBP i n promoting interactions between upstream promoter elements and the ba sal transcription apparatus.