Characterization of a two-component signal transduction system involved inthe induction of alkaline phosphatase under phosphate-limiting conditions in Synechocystis sp PCC 6803

The gene products of sll0337 and slr0081 in Synechocystis sp. PCC 6803 have been identified as the homologues of the Escherichia coli phosphate-sensin g histidine kinase PhoR and response regulator PhoB, respectively. Interrup tion of sll0337, the gene encoding the histidine protein kinase, by a spect inomycin-resistance cassette blocked the induction of alkaline phosphatase activity under phosphate-limiting conditions. A similar result was obtained when slr0081, the gene encoding the response regulator, was interrupted wi th a cassette conferring resistance to kanamycin. In addition, the phosphat e-specific transport system was not up-regulated in our mutants when phosph ate was limiting. Unlike other genes for bacterial phosphate-sensing two-co mponent systems, sll0337 and slr0081 are not present in the same operon. Al though there are three assignments for putative alkaline phosphatase genes in the Synechocystis sp. PCC 6803 genome, only sll0654 expression was detec ted by northern analysis under phosphate limitation. This gene codes for a 149 kDa protein that is homologous to the cyanobacterial alkaline phosphata se reported in Synechococcus sp. PCC 7942 [Ray, J.M., Bhaya, D., Block, M.A . and Grossman, A.R. (1991) J. Bact. 173: 4297-4309]. An alignment identifi ed a conserved 177 amino acid domain that was found at the N-terminus of th e protein encoded by sll0654 but at the C-terminus of the protein in Synech ococcus sp. PCC 7942.