All4312, an NtcA-regulated two-component response regulator in Anabaena sp. strain PCC 7120.

All4312, encoded by open reading frame all4312 in the genome of the heterocyst-forming cyanobacterium Anabaena sp. strain PCC 7120, exhibits a CheY-like receiver domain and an output domain similar to that of OmpR, characteristic of two-component response regulators. Expression of all4312 was directly regulated by NtcA, the global transcriptional regulator of nitrogen assimilation in cyanobacteria. Features characteristic of NtcA-activated promoters were also found upstream from genes encoding All4312 homologues in several other cyanobacterial genomes. Expression of all4312 was however unaffected in a mutant of hetR, which encodes a regulator triggering heterocyst development. The function of All4312 may be related to the cellular response to nitrogen deprivation.