The Synechococcus strain PCC 7942 glnN product (glutamine synthetase III) helps recovery from prolonged nitrogen chlorosis

We report the cloning and sequencing of the glnN gene encoding a class III glutamine synthetase from the cyanobacterium Synechococcus strain PCC 7942. Mapping of the transcriptional start site revealed a DNA sequence in the p romoter region that resembles an imperfect NtcA binding motif. Expression o f glnN is impaired in NtcA- and P-II-deficient mutants. The only parameter which was negatively affected in the glnN mutant compared to the wild type was the recovery rate of prolonged nitrogen starved cells with low concentr ations of combined nitrogen.