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Expression and heat‐responsive regulation of a TFIIB homologue from the archaeon Haloferax volcanii

Multiple divergent genes encoding the eukaryal‐like TFIIB (TFB) transcription initiation factor have been identified in the archaeon Haloferax volcanii. Expression of one of these TFB‐encoding genes, referred to here as tfb2, was induced specifically in response to heat shock at the transcription level. A time course for tfb2 induction demonstrated that mRNA levels increased as much as eightfold after 15 min at 60°C. A transcription fusion of the tfb2 promoter region with a stable RNA reporter gene confirmed the heat responsiveness of the tfb2 core promoter, and immunoblot analysis using antibodies generated against a recombinant His‐tagged TFB2 showed that the protein levels of one TFB increased slightly in response to elevated temperatures. An archaeal consensus TATA element (5′‐TTTATA‐3′) was located 110 bp upstream of the translation start site and appeared to be used for both basal and heat shock‐induced expression. The long DNA leader region (79 bp) preceding the predicted AUG translation start codon for TFB2 contained a T‐rich sequence element located 22 bp downstream of the transcription start site. Using an in vivo transcription termination assay, we demonstrated that this T‐rich element can function as a sequence‐dependent transcription terminator, which may serve to downregulate expression of the tfb2 gene under both non‐heat shock and heat shock conditions.