Transcriptional Regulation of the Heterocyst Patterning Gene patA from Anabaena sp. Strain PCC 7120

The filamentous cyanobacterium Anabaenasp. strain PCC 7120 forms a periodic pattern of nitrogen-fixing heterocystswhen grown in the absence of combined nitrogen. PatA is necessary for proper patterning of heterocystsalong 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. Localizationof a ringof 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.