Transcriptional regulation of zwf, encoding glucose-6-phosphate dehydrogenase, from the cyanobacterium Nostoc punctiforme strain ATCC 29133.

The gene encoding glucose-6-phosphate dehydrogenase (G6PD), zwf, in Nostoc punctiforme strain ATCC 29133 is part of a four-gene operon that also encodes fructose bisphosphatase (fbp), transaldolase (tal) and a gene product termed OpcA, which is contranscribed with zwf and essential for G6PD activity. The effect of exogenous nitrogen and carbon sources on transcription of these genes was investigated. Growth in the presence of ammonium yielded low levels of transcripts encoding all genes of the operon, while growth under nitrogen-fixing conditions resulted in a large increase of transcripts encoding for fbp and zwf-opcA. When cells are grown in the presence of fructose, levels of transcripts encoding tal and zwf-opcA were increased, relative to levels in ammonium-grown cells. These results indicate that this facultatively heterotrophic cyanobacterium can respond to changes in its environment by altering transcription of genes involved in carbon catabolism. Primer extension identified five 5' ends corresponding to the major regulated transcripts which we conclude arise from independent transcriptional start points.