| Research Abstract |
A His-kinases is a central player of a His→Asp phosphorelay signal transduction. In some case, however, another common histidine-containing phosphotransfer domain (or factor) plays a crucial role in a sequential His→Asp→His→Asp signaling event that is generally referred to as "multistep His→Asp phosphorelay". In this review, characteristic features of the HPt domain are discussed with special reference to the Escherichia coli ArcB hybrid His-kinase that contains the first discovered HPt domain. In E.coli physiology, this particular His-kinase is involved in the complex transcriptional regulatory network that allows E.coli cells to respond to various aerobic and anaerobic growth conditions. General views as to the widespread HPt domains are also discussed. As briefly overviewed here, a multistep His→Asp phosphorelay mechanism exerts a more sophisticated task than thought previously, in which a common HPt domains acts in concert with the classical two components, His-kinases and response regulators. Numerous instances of HPt domains can be predicted to occur in the current databases both for prokaryotes and eukaryotes, and their numbers are growing very rapidly. Nevertheless, their biological (or physiological) roles are virtually unknown, except the cases mentioned here. Since His→Asp phosphorelay signaling systems are so common and global both in prokaryotes and eukaryotes, they are the best paradigms of choice to explore through taking the newly developing post-sequencing approaches, such as DNA micro-array and proteome analyses
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