An oligomeric form of the large subunit of transcription factor (TF) IIE activates phosphorylation of the RNA polymerase II carboxyl-terminal domain by TFIIH

Phosphorylation of the COOH-terminal domain (CTD) of the largest subunit of RNA polymerase II by general transcription factor IIH (TFIIH) is believed to control the activity of polymerase at some stage of messenger RNA synthesis. In a recent study, transcription factor IIE (TFIIE) was proposed to play a key role in regulating phosphorylation of the RNA polymerase II CTD, on the basis of evidence indicating that preparations of recombinant TFIIE strongly stimulate CTD phosphorylation by TFIIH (Lu, H., Zawel, L., Fischer, L., Egly, J.-M., and Reinberg, D. (1992) Nature 358, 641-645). TFIIE is a heterodimer composed of 56-kDa (p56) and 34-kDa (p34) subunits and functions in concert with the TATA factor, TFIIB, TFIIF, and TFIIH to promote formation of the RNA polymerase II preinitiation complex. In the process of investigating the role that TFIIE plays in controlling phosphorylation of the RNA polymerase II CTD, we discovered that preparations of the recombinant TFIIE p56 subunit were sufficient to reconstitute stimulation of CTD phosphorylation by the TFIIH kinase. Further investigation revealed that CTD kinase stimulatory activity was chromatographically separable from the bulk of the transcriptionally active p56 subunit and was associated, instead, with a minor oligomeric form of p56. Taken together, these findings argue that the TFIIE p56 subunit is capable of interacting not only with the p34 subunit but also with itself to form either heterodimers or high molecular mass oligomers that play distinct roles in transcription initiation and regulation of the TFIIH kinase.