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

Abstract

The PII protein is encoded by a unique glnBgene 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 CO2and in the presence of nitrate under a high CO2concentration. Primer extension analysis indicated that the two transcript species are generated from two tandem promoters, a ς70 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 ς70 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.

Cellular acclimation strategies of a minimal picocyanobacterium to phosphate stress

“…P‐II is phosphorylated in cyanobacteria and as such interacts with both a phosphatase and a kinase. However, P‐II phosphatase interaction is thought to control nitrate/nitrite assimilation, and as MED4 is unable to grow on those particular nitrogen sources (Moore et al , 2002), and that the kinase activity is reduced when, in the presence of ammonia in another cyanobacterium, Synechococcus elongatus PCC7942 (Lee et al , 1999), this particular function of P‐II may well be redundant within MED4. With regard to amino acid synthesis, P‐II has been shown to increase N ‐acetyl glutamate kinase (NAGK) activity (Maheswaran et al , 2004), an enzyme in the arginine biosynthetic pathway, and identified in Synechococcus (Burillo et al , 2004; Heinrich et al , 2004).…”

NITROGEN STRESS RESPONSE OF PROCHLOROCOCCUS STRAIN PCC 9511 (OXYPHOTOBACTERIA) INVOLVES CONTRASTING REGULATION OF ntcA AND amt11

“…Evidence exists for the role of the cellular C-N balance and 2-oxoglutarate levels in sensing the nitrogen status in cyanobacteria (Lee et al 1999, Muro-Pastor et al 2001b). Furthermore, recent findings indicate that 2-oxoglutarate enhances the binding of NtcA to its promoter regions and is required for NtcA-induced transcription (Tanigawa et al 2002).…”

Protein PII regulates both inorganic carbon and nitrate uptake and is modified by a redox signal in Synechocystis PCC 6803

“…This interdependence raised the possibility that PII could play a role as a coordinator between 2‐oxoglutarate production, thence Ci assimilation, and nitrogen metabolism. As a support for this hypothesis, it has been found that growth of Synechococcus PCC 7942 on ammonium as nitrogen source with a high Ci concentration (HC), or in the presence of a low Ci concentration (LC) with nitrate, led to the unphosphorylated form of PII [3,9,10].…”