Abstract
Although a histidine kinase Hik33 in the cyanobacterium Synechocystis sp. PCC 6803 responds to various stress conditions and regulates the expression of several genes, it is not clear how it perceives the stimuli. In general, histidine kinase consists of two modules, a signal-input domain (SID) in the N-terminal region and a signal-transmitter domain in the C-terminal region. In order to analyze function of SID of Hik33 in vivo, we developed a technique to express a chimeric histidine kinase containing a SID from Hik33 and a signal-transmitter domain from a phosphate-deficient responding histidine kinase, SphS, in Synechocystis cells. The deletion of the PAS domain in the chimeric histidine kinase increased the activity of alkaline phosphatase whose expression was regulated via the chimeric histidine kinase. Then we substituted each 14 conserved amino acids in the PAS domain. Two of them decreased the kinase activity of the chimeric histidine kinase. These results indicate that the PAS domain of Hik33 is important for the fine-tuning of the kinase activity.
