Transcriptional regulation of the heterocyst patterning gene patA from Anabaena sp. strain PCC 7120.

The filamentous cyanobacterium Anabaena sp. strain PCC 7120 forms a periodic pattern of nitrogen-fixing heterocysts when grown in the absence of combined nitrogen. PatA is necessary for proper patterning of heterocysts along filaments. In this study, apparent transcriptional start points (tsps) were identified at nucleotides -305, -614, and -645 relative to the translational start site (-305, -614, and -645 tsps). Transcriptional reporter fusions were used to show that transcription from the -305 tsp was induced in all cells of filaments in response to nitrogen deprivation, required hetR for induction, and increased in a patA mutant. Transcription from -614/-645 tsp reporter fusions was spatially regulated and occurred primarily in cells that would become heterocysts. Complementation of a patA mutant strain by alleles encoding substitutions in, or deletion of, the putative phosphoacceptor C-terminal domain indicates that the PATAN domain can function independently of the C-terminal domain of PatA. Localization of a ring of PatA-GFP at sites of cell division, as well as the formation of enlarged cells with altered cell morphology when patA was overexpressed, suggests that PatA may participate in cell division.