Localized induction of the ntcA regulatory gene in developing heterocysts of Anabaena sp. strain PCC 7120.

The ntcA gene encodes an N-control transcriptional regulator in cyanobacteria. In the N(2)-fixing, heterocyst-forming cyanobacterium Anabaena sp. strain PCC 7120, ntcA is an autoregulatory gene that is transcribed from a complex promoter region that includes a constitutive promoter (P(2)) and promoters that are induced upon N step-down (P(1) and P(3)). Expression of ntcA was investigated with the use of an ntcA-gfp translational fusion, which was introduced both in the natural ntcA locus and in a heterologous genomic place. Induction of ntcA-gfp took place after N step-down in all the cells of the filament, but at especially high levels in developing heterocysts. Localized induction could be driven independently by P(3) and P(1).