Transcription of the glnB and glnA genes in the photosynthetic bacterium Rhodospirillum rubrum

The P-II protein, encoded by glnB, has a central role in the control of nitrogen metabolism in nitrogen-fixing prokaryotes. The glnB gene of Rhodospirillum rubrum was isolated and sequenced. The deduced amino acid sequence had very high sequence identity to other P-II proteins. The glnA gene, encoding glutamine synthetase, was located 135 bp downstream of glnB and was partially sequenced, glnB is cotranscribed with glnA from a promoter with high similarity to the sigma(54)-dependent promoter consensus sequence. A putative sigma(70) promoter was also identified further upstream of glnB. Northern blotting analyses showed that in addition glnA is either transcribed from an unidentified promoter or, more likely, that the glnBA transcript is processed to give the glnA mRNA. The total level of the two transcripts was much higher in nitrogen-fixing cells than in ammonia-grown cells.