Two distinct families of protein kinases are involved in signal transduction: Ser, Thr and Tyr kinases, which are predominantly found among eukaryotes, and His kinases, as part of bacterial two-component signalling systems. Genetic studies in Arabidopsis and Saccharomyces have demonstrated that bacterial-type two-component systems may act upstream of Ser/Thr kinases in the same signalling pathway, but how this coupling is accomplished remains unclear. In the present study, we report the characterization of a protein kinase, HstK, from the N2-fixing cyanobacterium Anabaena sp. PCC 7120, that possesses both a Ser/Thr kinase domain and a His kinase domain. Proteins with a structural architecture similar to that of HstK can be found in the eukaryote, Schizosaccharomyces pombe, and the bacterium, Rhodococcus sp. M5. HstK was present in cells grown with NH4+ or N2 as the nitrogen source, but was absent in cells grown with NO3−. The hstK gene was inactivated and the mutant phenotype was characterized. The catalytic domain of the Ser/Thr kinase of HstK functionally replaced that of Hog1p, a well-characterized protein kinase required for the response to high osmolarity in the S. cerevisiae heterologous system. The unusual multidomain structure of HstK suggests that a two-component system could be directly coupled to Ser/Thr kinases in the same signal transduction pathway.
HstK, a cyanobacterial protein with both a serine/threonine kinase domain and a histidine kinase domain: implication for the mechanism of signal transduction
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Vincent PHALIP, Jian-Hong LI, Cheng-Cai ZHANG; HstK, a cyanobacterial protein with both a serine/threonine kinase domain and a histidine kinase domain: implication for the mechanism of signal transduction. Biochem J 15 December 2001; 360 (3): 639–644. doi: https://doi.org/10.1042/bj3600639
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