Constitutive and nitrogen-regulated promoters of the petH gene encoding ferredoxin:NADP+ reductase in the heterocyst-forming cyanobacterium Anabaena sp.

Determination of the putative transcription start points of the petH gene encoding ferredoxin:NADP+ reductase in the heterocyst-forming cyanobacteria Anabaena sp. PCC 7119 and PCC 7120 showed that this gene is transcribed from two promoters, one constitutively used under different conditions of nitrogen nutrition and the other one used in cells subjected to nitrogen stepdown and in nitrogen-fixing filaments. The latter promoter, whose use was NtcA-dependent but HetR-independent, was functional in heterocysts. The N-control transcriptional regulator NtcA was observed to bind in vitro to this promoter. For the sake of comparison, the transcription start points of the nifHDK operon in strain PCC 7120 and binding of NtcA to the nifHDK promoter were also examined.