GSE51865
ChIP analysis unravels an exceptionally wide distribution of binding sites for the NtcA transcription factor in a heterocyst-forming cyanobacterium.
The CRP-family transcription factor NtcA, universally found in cyanobacteria, was initially discovered as a regulator operating N control. It responds to the N regime signaled by the internal 2-oxoglutarate levels, an indicator of the C to N balance of the cells. NtcA-activated canonical promoters bear an NtcA-consensus binding site (GTAN8TAC) centered at about 41.5 nucleotides upstream from the transcription start point. In this study, we have used chromatin immunoprecipitation followed by high-throughput sequencing to identify the whole regulon of NtcA in cells of the filamentous, heterocyst-forming cyanobacterium Anabaena sp. PCC 7120 after the withdrawal of combined N. NtcA has been found to bind to 2,424 target regions in the genome of Anabaena, which have been ascribed to 2,153 genes. Interestingly, only a small proportion of those are involved in N assimilation and metabolism, and 65 % of the target regions were located intragenically. The NtcA regulon identified here constitutes the largest bacterial regulon described to date. Our results show that NtcA has a much wider role in the physiology of the cell than it has been previously thought, acting both as a global transcriptional regulator and possibly also as a factor influencing the superstructure of chromosome (and plasmids). Overall design: Cells of Anabaena sp. PCC 7120 subjected to N-withdrawal for 3 h were used to perform chromatin immunoprecipitation with anti-NtcA antibody. The immunoprecipitated material was sequenced. Three ChIPs were performed from two independent sets of Anabaena cells. A sample of total DNA (not subjected to immunoprecipitation) was used as a control (Input sample).