Factors involved in specific transcription by mammalian RNA polymerase II. Identification and characterization of factor IIH.

Two new factors required for transcription of class II genes have been identified. These factors, TFIIH and TFIIJ, were required together with the previously described general factors (TFIIA, TFIIB, TFIID, TFIIE, and TFIIF) and RNA polymerase II for transcription of different class II genes. TFIIH was extensively purified, and the activity appeared to coelute with polypeptides of 33 and 95 kDa. The role of TFIIH and TFIIJ in preinitiation complex assembly was analyzed using mobility shift assays. It was found that TFIIH and TFIIJ association with the preinitiation complex was ordered and required the previous assembly of a preinitiation complex intermediate containing factors IID, IIB, IIF, IIE, and RNA polymerase II. A model for the ordered assembly of the general factors and RNA polymerase II is presented.