2-oxoglutarate enhances NtcA binding activity to promoter regions of the microcystin synthesis gene cluster

► New putative NtcA boxes identified in mcy promoters (Microcystis aeruginosa PCC7806). ► 2-oxoglutartate increased the affinity of NtcA for the mcyA promoter region. ► Data suggest that NtcA acts in this case as a repressor of microcystin synthesis. ► Data suggest that microcystin synthesis is regulated responding to the C/N balance. The binding affinity of NtcA towards promoter regions of the microcystin gene cluster from Microcystis aeruginosa PCC 7806 has been analyzed by band-shift assay (EMSA). The key nitrogen transcriptional regulator exhibits affinity for two fragments of the bidirectional mcyDA promoter, as well as for promoter regions of mcyE and mcyH. The presence of 2-oxoglutarate increased by 2.5 fold the affinity of NtcA for the mcyA promoter region. The 2-oxoglutarate effect peaked at 0.8 mM, a physiological concentration for this compound under nitrogen-limiting conditions. The results suggest that the 2-oxoglutarate level, as a signal of the C to N balance of the cells, regulates the microcystin gene cluster.