Transcription factor IIB (TFIIB) is an essential
component in the formation of the transcription initiation
complex in eucaryal and archaeal transcription. TFIIB interacts
with a promoter complex containing the TATA-binding protein
(TBP) to facilitate interaction with RNA polymerase II
(RNA pol II) and the associated transcription factor IIF
(TFIIF). TFIIB contains a zinc-binding motif near the N-terminus
that is directly involved in the interaction with RNA pol
II/TFIIF and plays a crucial role in selecting the transcription
initiation site. The solution structure of the N-terminal
residues 2–59 of human TFIIB was determined by multidimensional
NMR spectroscopy. The structure consists of a nearly tetrahedral
Zn(Cys)3(His)1 site confined by type
I and “rubredoxin” turns, three antiparallel
β-strands, and disordered loops. The structure is similar
to the reported zinc-ribbon motifs in several transcription-related
proteins from archaea and eucarya, including Pyrococcus
furiosus transcription factor B (Pf TFB),
human and yeast transcription factor IIS (TFIIS), and Thermococcus
celer RNA polymerase II subunit M (TcRPOM).
The zinc-ribbon structure of TFIIB, in conjunction with
the biochemical analyses, suggests that residues on the
β-sheet are involved in the interaction with RNA pol
II/TFIIF, while the zinc-binding site may increase the
stability of the β-sheet.