PHOSPHORYLATION IN HALOBACTERIAL SIGNAL-TRANSDUCTION

Regulated phosphorylation of proteins has been shown to be a hallmark of signal transduction mechanisms in both Eubacteria and Eukarya. Here we demonstrate that phosphorylation and dephosphorylation are also th e underlying mechanism of chemo- and phototactic signal transduction i n Archaea, the third branch of the living world. Cloning and sequencin g of the region upstream of the cheA gene, known to be required for ch emo- and phototaxis in Halobacterium salinarium, has identified cheY a nd cheB analogs which appear to form part of an operon which also incl udes cheA and the following open reading frame of 585 nucleotides. The CheY and CheB proteins have 31.3 and 37.5% sequence identity compared with the known signal transduction proteins CheY and CheB from Escher ichia coli, respectively. The biochemical activities of both CheA and CheY were investigated following their expression in E.coli, isolation and renaturation, Wildtype CheA could be phosphorylated in a time-dep endent manner in the presence of [gamma-P-32]ATP and Mg2+, whereas the mutant CheA(H44Q) remained unlabeled. Phosphorylated CheA was dephosp horylated rapidly by the addition of wild-type CheY, The mutant CheY(D 53A) had no effect on phosphorylated CheA. The mechanism of chemo- and phototactic signal transduction in the Archaeon H.salinarium, therefo re, is similar to the two-component signaling system known from chemot axis in the eubacterium E.coli.