This region is an all-alpha domain associated with the WD40 helical bundle of the TAF5 subunit of transcription factor TFIID. The domain has distant structural similarity to RNA polymerase II CTD interacting factors. It contains several conserved clefts that are likely to be critical for TFIID complex assembly [1]. The TAF5 subunit is present twice in the TFIID complex and is critical for the function and assembly of the complex, and the NTD2 and N-terminal domain is crucial for homodimerisation [2].

1: Structural analysis and dimerization potential of the human TAF5 subunit of TFIID. Bhattacharya S, Takada S, Jacobson RH; Proc Natl Acad Sci U S A. 2007;104:1189-1194. PMID:17227857

2: Crystal structure, biochemical and genetic characterization of yeast and E. cuniculi TAF(II)5 N-terminal domain: implications for TFIID assembly. Romier C, James N, Birck C, Cavarelli J, Vivares C, Collart MA, Moras D; J Mol Biol, 2007;368:1292-1306. PMID:17397863