A ROLE FOR TFIIH IN CONTROLLING THE ACTIVITY OF EARLY RNA-POLYMERASE-II ELONGATION COMPLEXES

TFIIH is a multifunctional RNA polymerase II transcription factor that possesses DNA-dependent ATPase, DNA helicase, and protein kinase acti vities, Previous studies have established that TFIIH enters the preini tiation complex and fulfills a critical role in initiation by catalyzi ng ATP-dependent formation of the open complex prior to synthesis of t he first phosphodiester bond of nascent transcripts, In this report, w e present direct evidence that TFIIH also controls RNA polymerase II a ctivity at a postinitiation stage of transcription, by preventing prem ature arrest by very early elongation complexes just prior to their tr ansition to stably elongating complexes, Unexpectedly, we observe that TFIIH is capable of entering the transcription cycle not only during assembly of the preinitiation complex hut also after initiation and sy nthesis of as many as four to six phosphodiester bonds, These findings shed new light on the role of TFIIH in initiation and promoter escape and reveal an unanticipated flexibility in the ability of TFIIH to in teract with RNA polymerase II transcription intermediates prior to, du ring, and immediately after initiation.