A Novel Archaeal Transcriptional Regulator of Heat Shock Response*

Archaea have a eukaryotic type of transcriptional machinery containing homologues of the transcription factors TATA-binding protein (TBP) and TFIIB (TFB) and a pol II type of RNA polymerase, whereas transcriptional regulators identified in archaeal genomes have bacterial counterparts. We describe here a novel regulator of heat shock response, Phr, from the hyperthermophilic archaeonPyrococcus furiosus that is conserved among Euryarchaeota. The protein specifically inhibited cell-free transcription of its own gene and from promoters of a small heat shock protein, Hsp20, and of an AAA+ ATPase. Inhibition of transcription was brought about by abrogating RNA polymerase recruitment to the TBP/TFB promoter complex. Phr bound to a 29-bp DNA sequence overlapping the transcription start site. Three sequences conserved in the binding sites of Phr, TTTA at −10, TGGTAA at the transcription start site, and AAAA at position +10, were required for Phr binding and are proposed as consensus regulatory sequences of Pyrococcus heat shock promoters. Shifting the growth temperature from 95 to 103 °C caused a dramatic increase of mRNA levels for theaaa+ atpase and phrgenes, but expression of the Phr protein was only weakly stimulated. Our findings suggest that heat shock response in Archaea is negatively regulated by a mechanism involving binding of Phr to conserved sequences.

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