Abstract
A histidine kinase (Hik) and a response regulator (Rre) consist a two-component system, which performs signal recognition and transduction pathway. In general, cyanobacteria contain more numbers of two-component systems per unit of genome size than other bacteria.
We identified functions of several Hiks and Rres in the cyanobacterium Synechocystis sp. PCC 6803. Among them, Hik33 is one of the most interesting Hiks, which might respond to several stimuli, such as cold, salt, hyperosmotic and oxidative stress, and transduces the stimuli to at least two Rres depending on the stimuli perceived. Moreover, Hik33 associated with a novel small protein, Ssl3451, which enhanced the in vitro activity of phosphorylation of Hik33 up to ten-fold. A disruptant of the ssl3451 gene indicated that it might also function in vivo as a regulator of Hik33. Hik33 and Ssl3451 are conserved in all the cyanobacterial genome, indicating that cyanobacteria develop unique features of two-component systems.
