Figure 3.

Coactivation by CBP and repression by p300 of vIRF transactivation of the MYC promoter. (A) CBP (4 μg) and p300 (4 μg) synergistically coactivate the interferon-β NF-κB enhancer promoter reporter pPRDII₄-Luc (2 μg) in combination with NF-κB p65 subunit (500 ng) in IRF1/2−/− MEF. A mutant CBP (CBP_F→A, 4 μg) with an amino acid substitution in the HAT domain is inactive. (B) Increasing amounts of CBP alone increase pBB-Luc transcription and synergistically coactivate with vIRF. Increasing amounts of p300, CBP_F→A, and P/CAF minimally affect pBB-Luc transcription alone but repress vIRF transactivation of pBB-Luc. For each experiment, 2 μg of reporter with or without 2 μg of pvIRF plasmids was used. Coadaptor amounts were 1 ng, 5 ng, 10 ng, 50 ng, 100 ng, and 1 μg of expression plasmids. (C) Model for coadaptor competition at the MYC promoter by p300 and CBP resulting in quenching of vIRF-induced transcription.