Accurate transcription initiation on TATA-containing class II genes involves the ordered assembly of RNA polymerase II (POLR2A; MIM 180660) and the general initiation factors TFIIA, TFIIB (MIM 189963), TFIID (MIM 313650), TFIIE (MIM 189962), TFIIF (MIM 189968), TFIIG/TFIIJ, and TFIIH (MIM 189972). The first step involves recognition of the TATA element by the TATA-binding subunit (TBP; MIM 600075) and may be regulated by TFIIA, a factor that interacts with both TBP and a TBP-associated factor (TAF; MIM 600475) in TFIID. TFIIA has 2 subunits (43 and 12 kD) in yeast and 3 subunits in higher eukaryotes. In HeLa extracts, it consists of a 35-kD alpha subunit and a 19-kD beta subunit encoded by the N- and C-terminal regions of GTF2A1 (MIM 600520), respectively, and a 12-kD gamma subunit encoded by GTF2A2.

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