Fig. 2.

Schematic model for TFIID assembly. a The histone fold containing TAFs form heterodimers and associates with TAF5 to form the core complex. The ability of TAF5 to homodimerise is still open to question, and it is as yet unclear whether the histone-like heterodimers associate to form higher order ‘lobe’ structures in the absence of TAF5. b TAF5 and the histone-like heterodimers associate to form the core complex. Variants of this complex in the form of 5 TAF (Drosophila S2 cells), 7 TAF (baculovirus reconstitution in vitro) or 9 TAF (yeast in vivo) complexes have been described and are discussed in the text. c The core complex interacts with the TAF1-TAF7-TBP sub-module to form TFIID. TAF2 may associate independently with TFIID through interaction with TAF1, but may not be always present in TFIID