THE STPA GENE FROM SYNECHOCYSTIS SP STRAIN PCC-6803 ENCODES THE GLUCOSYLGLYCEROL-PHOSPHATE PHOSPHATASE INVOLVED IN CYANOBACTERIAL OSMOTIC RESPONSE TO SALT SHOCK

Mutations in a gene, stpA, had been correlated with the loss of tolera nce to high NaCl concentrations in the cyanobacterium Synechocystis sp . strain PCC 6803. Genetic, biochemical, and physiological evidence sh ows that stpA encodes glucosylglycerol-phosphate phosphatase. stpA mut ants are salt sensitive and accumulate glucosylglycerol-phosphate, the precursor of the osmoprotectant glucosylglycerol necessary for salt a daptation of Synechocystis. The consensus motif present in acid phosph atases was found in StpA; however, the homology with other sugar phosp hatases is very poor. The amount of stpA mRNA was increased by growth of the cells in the presence of NaCl concentrations above 170 mM. Expr ession of stpA in Escherichia coli allowed the production of a 46-kDa protein which exhibited glucosylglycerol-phosphate phosphatase activit y. The StpA-specific antibody revealed a protein of similar size in ex tracts of Synechocystis, and the amount of this protein was increased in salt-adapted cells. The protein produced in E. coli had lost the re quirement for activation by NaCl that was observed for the genuine cya nobacterial enzyme.