Fos-Jun dimerization promotes interaction of the basic region with TFIIE-34 and TFIIF.

The regulation of RNA polymerase II-mediated transcription involves both direct and indirect interactions among regulatory proteins and the general transcription factors (GTFs) that assemble at TATA-containing promoters. Here we show that the oncogenic transcription factors Fos and Jun make direct physical contacts with three proteins of the basal transcription apparatus, TFIIE-34 (TFIIE-beta), TFIIF-30 (RAP30), and TFIIF-74 (RAP74). The interactions among the activator proteins and these three GTFs were not detected with other transcription factors, including some bZIP protein family members. Both coimmunoprecipitation and protein blotting experiments demonstrated that the interactions were strongly favored by dimerization of Fos and Jun and that they involved the basic region and basic region-proximal domain of both proteins. Mutations within the DNA-binding domains of Fos and Jun abolished binding to GTFs, although the presence of DNA was not required for the association. Surprisingly, only a single basic region in the context of a protein dimer was sufficient for the interaction. Squelching of AP-1-dependent transcription in vitro by an excess of Fos-Jun dimers was relieved by the addition of TFIIE, indicating that it is a direct functional target of Fos and Jun. These results suggest that dimerization induces a conformational alteration in the basic region of Fos and Jun that promotes an association with TFIIE-34 and TFIIF, thus contributing to transcription initiation.