Factors involved in specific transcription by mammalian RNA polymerase II. Factors IIE and IIF independently interact with RNA polymerase II.

The purification and characterization of transcription factor IIF (TFIIF), a factor required for transcription by the RNA polymerase II machinery, is described. TFIIF was isolated from the previously described IIE protein fraction. TFIIF enters into the transcription cycle via a preinitiation complex, and it is required for the formation of a complex capable of initiating transcription in the presence of heparin concentrations that inhibit the action of a free factor. TFIIF and TFIIE independently interacted with purified RNA polymerase II. TFIIF and TFIIE were both required for transcription of several class II promoters, including a promoter that lacks the conserved TATA box. Interestingly TFIIF was absolutely required for the formation of a preinitiation complex; however, it also affected the elongation phase of the transcription cycle. TFIIF, together with the previously described elongation factor TFIIS, was required for efficient elongation.