Structural domains comprising this superfamily share the structure of the alpha helical domain of the gamma subunit of the transcription factor IIA (TFIIA), which plays an important role in preinitiation complex (PIC) assembly in response to some transcriptional activators PMID:12972251.

Human and Drosophila TFIIA have three subunits: two large subunits, LN/alpha and LC/beta, derived from the same gene, and a small subunit, S/gamma. Yeast TFIIA on the other hand has two subunits: a large TOA1 subunit that shows sequence similarity to the N-terminal of LN/alpha and the C-terminal of LC/beta, and a small subunit, TOA2 that is highly homologous with S/gamma. This entry represents the alpha-helical domain found at the N-terminal of the gamma subunit of transcription factor TFIIA PMID:8610010.