CiteULike: cbg's ntca

Mutual dependence of the expression of the cell differentiation regulatory protein HetR and the global nitrogen regulator NtcA during heterocyst development

Alicia — 2008-05-09T14:33:23-00:00

Molecular Microbiology, Vol. 44, No. 5. (2002), pp. 1377-1385.

Summary Heterocyst differentiation in the cyanobacterium Anabaena sp. strain PCC 7120 depends on both the global nitrogen regulator NtcA and the cell differentiation regulatory protein HetR, and induction of hetR upon nitrogen step-down depends on NtcA. The use of two out of the four transcription start points (tsps) described for the hetR gene (those located at positions -728 and -271) was found to be dependent on NtcA, and the use of the tsp located at position -271 was also dependent on HetR. Thus, autoregulation of hetR could take place via the activation of transcription from this tsp. Expression of ntcA in nitrogen-fixing cultures was higher than in cells growing in the presence of ammonium or nitrate, and high expression of ntcA under nitrogen deficiency resulted from an increased use of tsps located at positions -180 and -49. The induction of the use of these tsps did not take place in ntcA or hetR mutant strains. These results indicate a mutual dependency in the induction of the regulatory genes hetR and ntcA that takes place in response to nitrogen step-down in Anabaena cells. Expression of the hetC gene, which is also involved in the early steps of heterocyst differentiation, from its NtcA-dependent tsp was, however, not dependent on HetR.

Requirement of the regulatory protein NtcA for the expression of nitrogen assimilation and heterocyst development genes in the cyanobacterium Anabaena sp. PCC7120

Jose Frias — 2008-05-08T22:16:25-00:00

Molecular Microbiology, Vol. 14, No. 4. (1994), pp. 823-832.

Summary The cyanobacterial ntcA gene encodes a DNA-binding protein that belongs to the Crp family of bacterial transcriptional regulators. In this work, we describe the isolation of an ntcA insertional mutant of the dinitrogen-fixing, heterocyst-forming cyanobacterium Anabaena sp. PCC 7120. The Anabaena ntcA mutant was able to use ammonium as a source of nitrogen for growth, but was unable to assimilate atmospheric nitrogen (dinitrogen) or nitrate. Nitrogenase and enzymes of the nitrate reduction system were not synthesized in the ntcA mutant under derepressing conditions, and glutamine synthetase levels were lower in the mutant than in the wild-type strain. In the ntcA mutant, in response to removal of ammonium, accumulation of mRNA of the genes encoding nitrogenase (nifHDK), nitrite reductase (nir, the first gene of the nitrate assimilation operon), and glutamine synthetase (glnA) was not observed. A transcription start point of the Anabaena glnA gene (corresponding to RNA1), that has been shown to be used preferentially after nitrogen step-down, was not used in the ntcA insertional mutant. Heterocyst development (which is necessary for the aerobic fixation of dinitrogen) and induction of hetR (a regulatory gene that is required for heterocyst development) were also impaired in the ntcA mutant. These results showed that the ntcA gene product, NtcA, is required in Anabaena sp. PCC 7120 for the expression of genes encoding proteins involved in the assimilation of nitrogen sources alternative to ammonium including dinitrogen and nitrate, and that the process of heterocyst development is also controlled by NtcA.

Anabaena sp. strain PCC 7120 ntcA gene required for growth on nitrate and heterocyst development.

TF Wei — 2008-04-17T00:30:28-00:00

J. Bacteriol., Vol. 176, No. 15. (1 August 1994), pp. 4473-4482.

The Anabaena sp. strain PCC 7120 ntcA (bifA) gene encodes a sequence-specific DNA-binding protein, NtcA (BifA, VF1) that interacts with the upstream region of several genes, including glnA, xisA, rbcL, and nifH. We have constructed a ntcA null mutant by interrupting the gene with an omega Spr-Smr cassette. The ntcA mutant was not able to grow with nitrate or atmospheric dinitrogen as the sole nitrogen source but could be grown on medium containing ammonium. The ntcA mutant was unable to form heterocysts and did not rearrange the nifD or fdxN elements after induction on a medium lacking combined nitrogen. Northern (RNA) analysis of ntcA in the wild-type strain during nitrogen stepdown showed a peak of ntcA message at an early stage (12 h) of heterocyst induction. Complementation of the ntcA mutant with a DNA fragment containing the ntcA gene and 251 bp of upstream sequence on a shuttle vector restored a wild-type phenotype; however, a similar construction containing 87 bp of upstream sequence only partially restored the phenotype. Northern analysis of RNA samples isolated from ammonium-grown cultures of the ntcA mutant showed reduced amounts of glnA message and the absence of a 1.7-kb transcript. In the wild type, the 1.7-kb transcript represents the majority of glnA transcripts after nitrogen stepdown. The ntcA mutant showed a normal pattern of rbcLS messages under these growth conditions.