A family of halobacterial transducer proteins.

A DNA probe to the signaling domain of a halobacterial transducer for phototaxis (HtrI) was used to clone and sequence four members of a new family of transducer proteins (Htps) in Halobacterium salinarium potentially involved in chemo- or phototactic signal transduction. The signaling domains in these proteins have 31-43% identity when compared with each other or with their bacterial analogs, the methyl-accepting chemotaxis proteins. An additional region of homology found in three of the Htps has 31-43% identity with HtrI. The Htps contain from 0 to 3 transmembrane helices and Western blotting showed that HtpIII is soluble. The arrangement of the domains in these Htps suggests a modular architecture in their construction.