NtcA, a global nitrogen regulator from the cyanobacterium Synechococcus that belongs to the Crp family of bacterial regulators

Abstract

The gene ntcA is required for full expression of proteins subject to ammonium repression in the cyanobacterium Synechococcus. A 3.1 kb DNA fragment able to complement an ntcA mutant was digested with exonuclease III, and deleted fragments of different size were tested for complementation of that mutant, allowing the localization of its mutation within a BamHI-HindIII genomic fragment of c. 0.4 kb. Insertion of a chloramphenicol-resistance-encoding gene cassette into both the BamHI and the HindIII sites of wild-type Synechococcus resulted in a pleiotropic, nitrogen-assimilation-minus phenotype, corroborating the presence of the ntcA gene in that genomic region. Sequencing of DNA in this region showed the presence of an open reading frame that included both the BamHI and the HindIII sites. The ntcA gene product, NtcA, is a protein of 24817 Da which belongs to a family of bacterial transcriptional activators that, among others, includes Crp and Fnr from Escherichia coli. Of special biological significance, it appears, is the presence of a conserved helix-turn-helix motif in the sequence close to the C-terminal end of all the proteins in the family. The gene ntcA is proposed to encode a transcriptional activator of genes subject to nitrogen control in Synechococcus.

Identification and nitrogen regulation of the cyanase gene from the cyanobacteria Synechocystis sp. strain PCC 6803 and Synechococcus sp. strain PCC 7942

“…Expression of ammonium-repressible genes of cyanobacteria generally requires NtcA, a Crp-type transcriptional activator protein (32). To determine whether transcription of cynS depends on NtcA, the levels of the cynS transcript in the wild-type strain and in an ntcA deletion mutant of strain PCC 7942 (29) were compared under the conditions for cynS induction (Fig.…”

Cloning, sequencing, and regulation of the global nitrogen regulator gene ntcA in the unicellular diazotrophic cyanobacterium Cyanothece sp. strain BH68K

“…The ntcA gene appears to be highly conserved in these organisms. The ntcA gene product, NtcA, belongs to the Crp family of bacterial transcriptional regulators (22). NtcA, like other members of this family, contains a characteristic helix-turn-helix motif near its C-terminal end which is believed to facilitate binding of NtcA directly to the promoter regions of nitrogen-regulated genes (22).…”

“…These 1,500-ml cultures were grown in 2-liter aspirator bottles to late exponential phase (A 750 of 0. 22) at 30°C, under a light intensity of 90 to 100 microeinsteins/m 2 /s, while being constantly bubbled with sterile moist air.…”

Effects of intermediate metabolite carboxylic acids of TCA cycle on Microcystis with overproduction of phycocyanin

“…The accumulation of alpha-ketoglutaric acid in the cyanobacterial cytoplasm, caused by shortage of nitrogen nutrients and high levels of photosynthesis, serves as the cellular signal for activation of NtcA, a FNR/CRP family global transcriptional regulator (Vega-Palas et al 1992). Alpha-ketoglutaric acid (KGA) is a key intermediate in the TCA cycle and major contributor to amino and protein metabolism.…”

“…Alpha-ketoglutaric acid (KGA) is a key intermediate in the TCA cycle and major contributor to amino and protein metabolism. Under shortage of ammonium, KGA cannot be converted into glutamine and accumulate in the cytoplasm (Vega-Palas et al 1992). NtcA regulates a series of crucial cellular processes such as nitrogen uptake and/or nitrogen fixation as well as the microcystin biosynthesis in Microcystis and other cyanobacteria.…”