An archaeal aerotaxis transducer combines subunit I core structures of eukaryotic cytochrome c oxidase and eubacterial methyl-accepting chemotaxis proteins.

Signal transduction in the archaeon Halobacterium salinarum is mediated by three distinct subfamilies of transducer proteins. Here we report the complete htrVIII gene sequence and present analysis of the encoded primary structure and its functional features. HtrVIII is a 642-amino-acid protein and belongs to halobacterial transducer subfamily B. At the N terminus, the protein contains six transmembrane segments that exhibit homology to the heme-binding sites of the eukaryotic cytochrome c oxidase. The C-terminal domain has high homology with the eubacterial methyl-accepting chemotaxis protein. The HtrVIII protein mediates aerotaxis: a strain with a deletion of the htrVIII gene loses aerotaxis, while an overproducing strain exhibits stronger aerotaxis. We also demonstrate that HtrVIII is a methyl-accepting protein and demethylates during the aerotaxis response.