Enhanceosome-CBP interactions are required for the efficient recruitment of the RNA polymerase II holoenzyme to the preinitiation complex. (A and B) Immobilized IFN-β enhancer DNA template was incubated with TFIID, TFIIA, TFIIB, USA and RNA polymerase II holoenzyme in the absence or presence of an IFN-β enhanceosome assembled by using purified recombinant proteins ATF2/c-JUN, IRF1, p50/p65 of NF-κB and HMG I(Y). Increasing amounts of the anti-CBP antibody (α CBP) were preincubated with the RNA polymerase II holoenzyme before mixing with all the other components. (A) Promoter complexes were purified and analyzed for transcription in the presence of NTPs. (B) The amounts of template-bound factors TBP, TFIIB (IIB), CBP, TFIIEα (IIE), RNA polymerase II (POL II), and SRB7 were determined by immunoblotting assays after washing promoter complexes.