Dissection of the regulatory mechanism of a heat-shock responsive promoter in Haloarchaea: a new paradigm for general transcription factor directed archaeal gene regulation.

Multiple general transcription factors (GTFs), TBP and TFB, are present in many haloarchaea, and are deemed to accomplish global gene regulation. However, details and the role of GTF-directed transcriptional regulation in stress response are still not clear. Here, we report a comprehensive investigation of the regulatory mechanism of a heat-induced gene (hsp5) from Halobacterium salinarum. We demonstrated by mutation analysis that the sequences 5' and 3' to the core elements (TATA box and BRE) of the hsp5 promoter (P(hsp5)) did not significantly affect the basal and heat-induced gene expression, as long as the transcription initiation site was not altered. Moreover, the BRE and TATA box of P(hsp5) were sufficient to render a nonheat-responsive promoter heat-inducible, in both Haloferax volcanii and Halobacterium sp. NRC-1. DNA-protein interactions revealed that two heat-inducible GTFs, TFB2 from H. volcanii and TFBb from Halobacterium sp. NRC-1, could specifically bind to P(hsp5) likely in a temperature-dependent manner. Taken together, the heat-responsiveness of P(hsp5) was mainly ascribed to the core promoter elements that were efficiently recognized by specific heat-induced GTFs at elevated temperature, thus providing a new paradigm for GTF-directed gene regulation in the domain of Archaea.