2‐Oxoglutarate increases the binding affinity of the NtcA (nitrogen control) transcription factor for the <i>Synechococcus glnA</i> promoter

Abstract

The cyanobacterial NtcA global nitrogen regulator belongs to the catabolite activator protein (CAP) family and activates transcription of nitrogen assimilation genes in response to nitrogen step-down. The binding affinity of NtcA towards a DNA fragment carrying the promoter of the glnA gene from Synechococcus sp. PCC 7942, analyzed in vitro by band-shift assay, was increased five-fold by 2-oxoglutarate in the presence of Mg(2+) ions. The 2-oxoglutarate effect peaked at about 0.6 mM, a rather physiological concentration for this compound under nitrogen-limiting conditions, and could be partially reproduced by 3-oxoglutarate but not by oxaloacetate or glutamate. These results suggest 2-oxoglutarate as a signal of the C to N balance of the cells to regulate NtcA activity and provide a new example of regulation in the versatile CAP family of proteins.