Journal article

Publication year: 2000

Pages: 591-600

Journal: European Journal of Biochemistry

Volume number: 267

Issue number: 2

ISSN: 0014-2956

Open access status: Bronze

DOI Link: https://doi.org/10.1046/j.1432-1327.2000.01043.x

Publisher: Wiley: No OnlineOpen

Abstract: 
In the cyanobacterium Synechococcus sp. strain PCC 7942, the phosphorylation states of the signal transducer P-II protein (GlnB) can change rapidly depending on the nitrogen and carbon supply. A P-II-null mutant (MP2) shows no ammonium-dependent inhibition of the nitrate and nitrite uptake, in contrast to the wild-type. New mutants with different types of P-II, which may mimic either the phosphorylated (GlnB(S49E) or GlnB(S49D)) or unphosphorylated (GlnB(S49A)) form of the protein, were constructed using site-directed in vitro mutagenesis. Mutant MP2-A (GlnB(S49A)) grew poorly using nitrate as a nitrogen source and was unable to take up nitrate supplied at 100 mu M, even in the absence of externally added ammonium. Mutants MP2-D and MP2-E (GlnB(S49D) and GlnB(S49E), respectively), however, showed nitrate-dependent growth and regulation of nitrate uptake by ammonium, as in the wild-type. Characterization of the mutants also included an analysis of nitrite uptake and of the levels of the nir (nitrate/nitrite assimilation) operon transcripts, the presence of NrtA (nitrate/nitrite transport binding protein), and nitrate and nitrite reductase activities. In vitro, no significant difference was observed in the cooperative binding of ATP and 2-oxoglutarate between the wild-type and the unphosphorylated or phosphorylated-like forms of the mutant P-II proteins. The results obtained indicate that both unphosphorylated and phosphorylated-like forms of P-II are able to inhibit nitrate uptake in the presence of ammonium, but the unphosphorylated form also has a negative effect in the absence of this nitrogen source. Therefore, an additional effector, possibly 2-oxoglutarate, is required for the P-II protein to relieve inhibition of nitrate uptake in the absence of ammonium.

Harvard Citation style: Lee, H., Flores, E., Forchhammer, K., Herrero, A. and de Marsac, N. (2000) Phosphorylation of the signal transducer P_II protein and an additional effector are required for the P_II-mediated regulation of nitrate and nitrite uptake in the cyanobacterium Synechococcus sp PCC 7942, European Journal of Biochemistry, 267(2), pp. 591-600. https://doi.org/10.1046/j.1432-1327.2000.01043.x

APA Citation style: Lee, H., Flores, E., Forchhammer, K., Herrero, A., & de Marsac, N. (2000). Phosphorylation of the signal transducer P_II protein and an additional effector are required for the P_II-mediated regulation of nitrate and nitrite uptake in the cyanobacterium Synechococcus sp PCC 7942. European Journal of Biochemistry. 267(2), 591-600. https://doi.org/10.1046/j.1432-1327.2000.01043.x