Transcription initiation factor IIA (TFIIA) is a heterotrimer, the three subunits being known as alpha, beta, and gamma, in order of molecular weight. The N and C-terminal domains of the gamma subunit are represented in Pfam:PF02268 and Pfam:PF02751, respectively. This family represents the precursor that yields both the alpha and beta subunits. The TFIIA heterotrimer is an essential general transcription initiation factor for the expression of genes transcribed by RNA polymerase II. Together with TFIID, TFIIA binds to the promoter region; this is the first step in the formation of a pre-initiation complex (PIC). Binding of the rest of the transcription machinery follows this step [1]. After initiation, the PIC does not completely dissociate from the promoter. Some components, including TFIIA, remain attached and re-initiate a subsequent round of transcription.

1: A transcription reinitiation intermediate that is stabilized by activator. Yudkovsky N, Ranish JA, Hahn S; Nature 2000;408:225-229. PMID:11089979

2: A single cDNA, hTFIIA/alpha, encodes both the p35 and p19 subunits of human TFIIA. DeJong J, Roeder RG; Genes Dev 1993;7:2220-2234. PMID:8224848

3: Crystal structure of a yeast TFIIA/TBP/DNA complex. Tan S, Hunziker Y, Sargent DF, Richmond TJ; Nature 1996;381:127-151. PMID:8610010