Protein PII regulates both inorganic carbon and nitrate uptake and is modified by a redox signal in Synechocystis PCC 6803

In Synechocystis PCC 6803 as in other cyanobacteria. involvement of protein PII in the co-regulation of inorganic carbon and nitrogen metabolism was e stablished based on posttranslational modifications of the protein resultin g from changes in the carbon/nitrogen regimes. Uptake of bicarbonate and ni trate in response to changes of the carbon and/or nitrogen regimes is alter ed in a PII-null. mutant, indicating that both processes are under control of PII. Modulation of electron flow by addition of methyl viologen with or without duroquinol, or in a NAD(P)H dehydrogenase-deficient mutant, affects the phosphorylation level of PII. The redox state of the cells would thus act as a trigger for PII phosphorylation. (C) 1999 Federation of European B iochemical Societies.