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ChIP analysis unravels an exceptionally wide distribution of binding sites for the NtcA transcription factor in a heterocyst-forming cyanobacterium.

ABSTRACT: 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).

ORGANISM(S): Anabaena

PROVIDER: GSE51865 | GEO | 2014/01/28

SECONDARY ACCESSION(S): PRJNA225619

REPOSITORIES: GEO

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ChIP analysis unravels an exceptionally wide distribution of binding sites for the NtcA transcription factor in a heterocyst-forming cyanobacterium.

Project description: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). 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).

2014-01-28 | E-GEOD-51865 | biostudies-arrayexpress

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Elucidating the direct target regulon of NtcA during the early acclimation to nitrogen starvation in the cyanobacterium Synechocystis sp. PCC 6803 [RNA-Seq]

Project description:Cyanobacteria are oxygenic photoautotrophs responsible for a substantial proportion of nitrogen fixation and primary production in the hydrosphere. Non-nitrogen fixing cyanobacteria, such as Synechocystis sp. PCC 6803, depend of the availability of nitrogenized species to survive. Therefore, an intricate regulatory network around the transcriptional factor NtcA maintains the homeostasis of nitrogen in these organisms. The mechanisms controlling NtcA activity are well understood but a comprehensive study of its regulon is missing in Synechocystis. To define NtcA regulon during the early stage of nitrogen starvation, we have performed chromatin immunoprecipitation followed by sequencing (ChiP-seq), in parallel with genome level transcriptome analysis (RNA-seq). By combining both methods we assigned 51 activated and 28 repressed genes directly by NtcA. Most of direct targets included genes involved in nitrogen and carbon metabolism and photosynthesis. NtcA regulon also included 8 ncRNAs, of which ncr0710, Syr6 and NsiR7 were experimentally validated. Intriguingly, we identified several NtcA intragenic binding sites suggesting that NtcA can modulate transcriptional expression by binding along the whole transcript and not only in the promoter region as previously though. Finally, the transcriptional implication of PipX was analyzed in some NtcA-targets genes, revealing that PipX assists NtcA in the global nitrogen regulation in Synechocystis.

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