TFIIF beta subunit HTHisIPR040450. In addition to RNA polymerase II, a minimum of six general transcription initiation factors are necessary for accurate transcription in vivo. A tetramer comprising two large subunits (TFIIF α or RAP74) and two small subunits (TFIIF β or RAP30) is known as transcription initiation factor IIF (TFIIF). The recruitment of RNA polymerase II to the promoter is contingent upon the presence of the β subunit of TFIIF.