Molecular Mechanism of Signal Transduction in Prokaryotes

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Recently we demonstrated the occurrence of a novel device of signal transducers in Escherichia coli. Among such E.coli signal transducers, the arcB is of particular interest, because these proteins are unique in the sense that they contain both an autophosphorylated histidine site (or transmitter module) and a phospho-accepting aspartate site (or receiver module) in their primary amino acid sequences. ArcB was originally characterized as the signal transducer involved in anaerobic repression of regulons of the aerobic function. We demonstrated that ArcB possesses in the C-terminal region another phosphorylated histidine site, in addition to the previously indentified authentic one. It was demonstrated for ArcB that the C-terminal domain containing the histidine (His-717) can function as an alternative phosphodonor (a truncated form of ArcB containing this C-terminal region was previously designated as ArcB^C). This novel type of sensory kinases was revealed to contain two phosphorylated histidine sites together with a phospho-accepting asparatate site. It is therefore most likely that ArcB can make a complex phosphotransfer circuitry. Furthermore, our resuls supported the view that ArcB can serve as a powerful device for not only propagating multi-signals but also making up signaling networks through more sophisticated manners than thought previously.