A TRANSCRIPTION FACTOR IIB HOMOLOG FROM THE HYPERTHERMOPHILIC ARCHAEON PYROCOCCUS-FURIOSUS BINDS ZN OR FE IN N-TERMINAL CYS(4) MOTIF

The gene for an archael homolog of the eukaryotic transcription factor TFIIB has been cloned from the marine hyperthermophilic archaeon Pyro coccus furiosus and overexpressed in Escherichia coli. This TFB gene d isplays a sequence that is identical to a gene sequence in P. woesei. A gene for the 49-residue N-terminal domain of TFB that contains a put ative C-X(2)-C-X(15)-C-X(2)-C metal-binding motif was subcloned and ov erexpressed as TFB-NTD. Purification of the TFB-NTD gene product yield s Zn- and Fe-containing forms, which have been characterized by mass s pectrometry and UV-visible, electron paramagnetic resonance, and X-ray absorption (XAS) spectroscopies. Only the Zn form of the TFB holoprot ein has been (partially) purified, and it has been characterized by XA S. All spectroscopic characteristics are consistent with a nearly tetr ahedral MS(4) metal-binding site made up or the four cysteine residues in the N-terminal domain. The relatively greater thermal stability of the Zn form suggests that TFB may be a Zn-containing protein involved in archaeal transcription.