Human transcription initiation factor TFIID is composed of the TATA-binding protein (TBP) and at least 13 TBP-associated factors (TAFs) that collectively or individually are involved in activator-dependent transcription. Initiation of transcription by RNA polymerase II requires the ordered assembly of basal transcription factors including TFIIA, TFIIB, TATA-binding protein (TBP), TFIIE, TFIIF, TFIIG/TFIIJ, and TFIIH/BTF2 into the TFIID complex. Different activators may interact with specific TAFs to allow the assembly of functionally distinct TFIID complexes that can control transcription of different genes. (NCI) [ ]