Abstract
We have investigated functions of histidine kinases in Synechocystis sp. PCC 6803 by analyzing phenotypes of the mutants. However, there remain some histidine kinases that are functionally unknown because of the difficulty to obtain the mutants. We tried to characterize one of the essential histidine kinases, Hik2, by constructing a chimera sensor which has signal-input domain of Hik2 and kinase domain of SphS responsive to phosphate-deficiency. We replaced coding region of the sphS gene with the chimera sensor. It allowed us to evaluate activity of the Hik2-SphS chimera as the activity of alkaline phosphatase (AP) regulated originally by SphS.
The cells possessing the chimera sensor had a slight AP activity under the standard growth conditions. Although salt stress due to NaCl induced the AP activity in a dose-dependent manner, other types of stress, such as high light, osmotic and oxidative, did not. It suggested that Hik2 is related to responsiveness to salt stress. Replacements of conserved amino-acids in Hik2 region of the chimeric sensor lost the activity, suggesting that these residues might be involved in the mechanisms of salt sensing.
