Heat shock inducibility of an archaeal TATA-like promoter is controlled by adjacent sequence elements

The expression of a heat-inducible cct1 (chaperonin-containing Tcp-1) family member gene is regulated at the transcription level in the archaeon Haloferax volcanii. Transcriptional fusions of the cct1 promoter region with a yeast proline tRNA reporter gene were constructed to analyse the functional domains of this archaeal heat shock promoter. Both basal and heat-induced transcription of the reporter gene was directed by an archaeal consensus TATA element (5'-TTTATA-3') centred 25 bp upstream of the transcription start site. Deletion mutagenesis indicated that the 5' boundary of the cct1 regulatory region mapped to position -37. Nucleotide alignment with the 5' flanking regions of two additional cct-related genes identified in H. volcanii showed a high degree of sequence conservation between positions +1 and -37, especially in and immediately surrounding the TATA element of the putative core promoter. Mutational analysis of conserved sequences demonstrated that basal and heat-induced transcription required sequence elements located upstream and downstream of the TATA-box. These findings indicate that the regulatory sequences involved in heat-induced transcription lie within the core promoter region and suggest that the mechanism controlling heat shock gene expression in H. volcanii differs from the bacterial and eukaryal strategies.