Regulation in the Archaea

The expression of two heat-responsive cct (chaperonin-containing Tcp-1) genes from the archaeon Haloferax volcanii was investigated at the transcription level. The cct1 and cct2 genes, which encode proteins of 560 and 557 amino acids, respectively, were identified on cosmid clones of an H. volcanii genomic library and subse-quently sequenced. The deduced amino acid sequences of these genes exhibited a high degree of similarity to other archaeal and eucaryal cct family members. Expression of the cct genes was characterized in detail for the purpose of developing a model for studying transcription regulation in the domain Archaea. Northern (RNA) analysis demonstrated that the cct mRNAs were maximally induced after heat shock from 37 to 55°C and showed significant heat inducibility after 30 min at 60°C. Transcription of cct mRNAs was also stimulated in response to dilute salt concentrations. Transcriptional analysis of cct promoter regions coupled to a yeast tRNA reporter gene demonstrated that 5 * flanking sequences up to position 2233 (cct1) and position 2170 (cct2) were sufficient for promoting heat-induced transcription. Transcript analysis indicated that both basal transcrip-tion and stress-induced transcription of the H. volcanii cct genes were directed by a conserved archaeal consensus TATA motif (5*-TTTATA-3*) centered at 225 relative to the mapped initiation site. Comparison of the cct promoter regions also revealed a striking degree of sequence conservation immediately 5 * and 3 * of the TATA element