CHEMOTAXIS AND PHOTOTAXIS REQUIRE A CHEA HISTIDINE KINASE IN THE ARCHAEON HALOBACTERIUM-SALINARIUM

Histidine kinases are part of the two-component signal transduction sy stem responsible for eubacterial responses to diverse environmental si gnals, They have recently been detected in eukaryotes but their existe nce in the kingdom Archaea remains uncertain, Here we report the seque nce and function of a histidine kinase (CheA(H.s.)) from Halobacterium salinarium, the first such transmitter in Archaea. The protein CheA(H .s.) (668 residues) has significant sequence identity with the CheA pr oteins known from eubacterial signal transduction (e.g, 34% identity w ith CheA from Bacillus subtilis). Antibodies were raised against CheA( H.s.), as expressed in Escherichia coli and were used in Western blott ing to demonstrate the expression of cheA(H.s.) in H.salinarium. As ha s been observed for other halophilic proteins, CheA(H.s.) has a devian t electrophoretic migration, with an apparent molecular weight of 103 kDa on SDS-PAGE compared with a calculated molecular weight of 72 kDa, Deletion of a part of the cheA(H.s.) gene leads to loss of both chemo tactic and phototactic responses in H.salinarium as measured by swarm plate assays, motion analysis and tethering experiments, This indicate s that CheA(H.s.) plays a crucial role in chemical and light signal in tegration, presumably interacting with at least two phototransducers a nd a number of chemoreceptors.