Nitrogen deprivation of Anabaena sp. strain PCC 7120 elicits rapid activation of a gene cluster that is essential for uptake and utilization of nitrate.

A transposon bearing luxAB, encoding luciferase, as a reporter of transcription was used to identify genes that are activated rapidly upon deprivation of Anabaena sp. strain PCC 7120 of fixed nitrogen. The three transposon-marked loci that were identified as responding most rapidly and strongly are closely linked and situated within nirA and nrtC and between nrtD and narB, genes whose products are responsible for uptake and reduction of NO2- and NO3-. A strain bearing a transcriptional fusion of narB to luxAB was constructed. Luminescence catalyzed by LuxAB was used to report on the expression of the interrupted genes. Whether these genes are regulated only coordinately is discussed.