BIOCHEMISTRY AND STRUCTURAL BIOLOGY OF TRANSCRIPTION FACTOR-IID (TFIID)

Eukaryotes have three distinct RNA polymerases that catalyze transcrip tion of nuclear genes. RNA polymerase II is responsible for transcribi ng nuclear genes encoding the messenger RNAs and several small nuclear RNAs. Like RNA polymerases I and III, pol II cannot recognize its tar get promoter directly and initiate transcription without accessory fac tors. Instead, this large multisubunit enzyme relies on both general t ranscription factors and transcriptional activators and coactivators t o regulate transcription from class II promoters. At the center of thi s process is TFIID, a 700-kD complex composed of the TATA box binding protein (TBP) and a set of phylogenetically conserved, polymerase-spec ific TBP-associated factors or TAF(II)s. Together, TBP and the TAF(II) s direct assembly of the transcription machinery and play critical reg ulatory roles in eukaryotic gene expression.