Interaction of the COOH-terminal transactivation domain of p65 NF-kappa B with TATA-binding protein, transcription factor IIB, and coactivators.

We show that the transactivating COOH terminus of the p65 subunit of human transcription factor NF-kappa B directly binds the general transcription factors TFIIB and TATA-binding protein (TBP) in vitro. Interaction of p65 with TFIIB required the most COOH-terminal sequence repeat within TFIIB. A functional interaction of TFIIB with p65 was evident from assays in yeast cells. Cotransfection experiments in COS cells revealed that only overexpression of TBP was able to further stimulate p65-dependent transactivation of a reporter gene. The coexpression of neither TBP nor TFIIB was able to relieve squelching, indicating the involvement of additional factors in transactivation by p65. A cell-free assay using highly purified factors revealed a specific transcriptional stimulation through the COOH-terminal activation domain of NF-kappa B by at least one cofactor, PC1, isolated from HeLa cells. These data show that the potent acidic transactivation domains in the COOH terminus of p65 are able to functionally recruit various components of the basic transcription machinery as well as coactivators.