Factors involved in specific transcription by mammalian RNA polymerase II. Purification and subunit composition of transcription factor IIF.

Transcription factor IIF (TFIIF), a protein factor required for transcription of class II genes, has been purified to near homogeneity. TFIIF is a heterodimer of 30- and 78-kDa polypeptides. Both the 30- and 78-kDa polypeptides were necessary to reconstitute TFIIF activity. TFIIF activity eluted from a gel filtration column with an apparent molecular mass of 220 kDa, suggesting that the native factor exists as a dimer of the heterodimer.