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Journal of Bacteriology, May 1999, p. 2697-2702, Vol. 181, No. 9
0021-9193/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.

The Global Nitrogen Regulator NtcA Regulates Transcription of the Signal Transducer PII (GlnB) and Influences Its Phosphorylation Level in Response to Nitrogen and Carbon Supplies in the Cyanobacterium Synechococcus sp. Strain PCC 7942

Hyun-Mi Lee,1 María Félix Vázquez-Bermúdez,2 and Nicole Tandeau de Marsac1,*

Département de Biochimie et Génétique Moléculaire, Unité de Physiologie Microbienne, Institut Pasteur, 75724 Paris Cedex 15, France,1 and Instituto de Bioquímica Vegetal y Fotosíntesis, CSIC-Universidad de Sevilla, Centro de Investigaciones Científicas Isla de la Cartuja, E-41092, Seville, Spain2

Received 3 December 1998/Accepted 12 February 1999

The PII protein is encoded by a unique glnB gene in Synechococcus sp. strain PCC 7942. Its expression has been analyzed in the wild type and in NtcA-null mutant cells grown under different conditions of nitrogen and carbon supply. RNA-DNA hybridization experiments revealed the presence of one transcript species 680 nucleotides long, whatever the nutrient conditions tested. A second transcript species, 620 nucleotides long, absent in the NtcA null mutant, was observed in wild-type cells that were nitrogen starved for 2 h under both high and low CO2 and in the presence of nitrate under a high CO2 concentration. Primer extension analysis indicated that the two transcript species are generated from two tandem promoters, a sigma 70 Escherichia coli-type promoter and an NtcA-dependent promoter, located 120 and 53 nucleotides, respectively, from the glnB initiation codon. The NtcA-dependent promoter is up-regulated under the conditions mentioned above, while the sigma 70 E. coli-type promoter displays constitutive levels of transcripts in the NtcA null mutant and slightly different levels in the wild-type cells, depending on the nitrogen and carbon supplies. In general, a good correlation between the amounts of the two transcript species and that of the PII protein was observed, as revealed by immunodetection with specific antibodies. The phosphorylation level of PII in the wild type is inversely correlated with nitrogen availability and directly correlated with higher CO2 concentration. This regulation is correspondingly less stringent in the NtcA null mutant cells. In contrast, the dephosphorylation of PII is NtcA independent.

* Corresponding author. Mailing address: Département de Biochimie et Génétique Moléculaire, Unité de Physiologie Microbienne, Institut Pasteur, 28 rue du Docteur Roux, 75724 Paris Cedex 15, France. Phone: 33 (0)1 45 68 8415. Fax: 33 (0)1 40 61 3042. E-mail: ntmarsac{at}pasteur.fr.

Journal of Bacteriology, May 1999, p. 2697-2702, Vol. 181, No. 9
0021-9193/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.


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