TFIIB domains for interaction with TFIID/TATA complex
TFIIB has two fundamental activities : (i) formation of TFIID-TFIIB/TATA complex (also called D-B DNA complex) and (ii) basal transcription. In the year 1993, deletion mutants of TFIIB were used to identify the domains responsible for the above two activities. Following two domains were identified for specific functional roles : (i) The C-terminal domain, containing two direct repeats and two basic residue repeats is necessary and sufficient for interaction with TFIID/TATA complex (also called D-DNA complex). In the absence of TFIID, TFIIB did not bind DNA suggesting that an interaction between TFIIB and TFIID takes place, (ii) An extra 84-residue N-terminal region (which is not needed for the formation of D-B complex) is required for basal transcriptional activity, so that in the absence of this region, despite the formation of D-B complex, transcription was greatly reduced or completely stopped. This region may, therefore, be involved in, the recruitment of RNA polymerase II to the complex. It has been shown that in TFIIB and TFIID, similar structural domains are present for protein-DNA interaction (these similarities include C-terminal direct repeats, basic residue repeats, sigma homologies).