The poor growth of Rhodospirillum rubrum mutants lacking PII proteins is due to an excess of glutamine synthetase activity.
The P(II) family of proteins is found in all three domains of life and serves as a central regulator of the function of proteins involved in nitrogen metabolism, reflecting the nitrogen and carbon balance in the cell. The genetic elimination of the genes encoding these proteins typically leads to severe growth problems, but the basis of this effect has been unknown except with Escherichia coli. We have analysed a number of the suppressor mutations that correct such growth problems in Rhodospirillum rubrum mutants lacking P(II) proteins. These suppressors map to nifR3, ntrB, ntrC, amtB(1) and the glnA region and all have the common property of decreasing total activity of glutamine synthetase (GS). We also show that GS activity is very high in the poorly growing parental strains lacking P(II) proteins. Consistent with this, overexpression of GS in glnE mutants (lacking adenylyltransferase activity) also causes poor growth. All of these results strongly imply that elevated GS activity is the causative basis for the poor growth seen in R. rubrum mutants lacking P(II) and presumably in mutants of some other organisms with similar genotypes. The result underscores the importance of proper regulation of GS activity for cell growth.
Zhang
Yaoping
Y
Department of Bacteriology, Center for the Study of Nitrogen Fixation, University of Wisconsin-Madison, Madison, WI 53706, USA.
Pohlmann
Edward L
EL
Conrad
Mary C
MC
Roberts
Gary P
GP
D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D004251:DNA Transposable Elements; D015964:Gene Expression Regulation, Bacterial; D016153:Genes, Suppressor; D005974:Glutamate-Ammonia Ligase / Q000235:genetics / Q000378:metabolism*; D016254:Mutagenesis, Insertional; D009154:Mutation; D009713:Nucleotidyltransferases / Q000235:genetics / Q000378:metabolism; D051922:PII Nitrogen Regulatory Proteins / Q000235:genetics / Q000378:metabolism; D012247:Rhodospirillum rubrum / Q000235:genetics / Q000254:growth & development* / Q000378:metabolism
D001426:Bacterial Proteins; D004251:DNA Transposable Elements; C439048:GlnJ protein, Rhodospirillum rubrum; D051922:PII Nitrogen Regulatory Proteins; C083572:ntrB protein, Rhizobium; C083573:ntrC protein, Rhizobium; C404143:PIID regulatory protein, Bacteria; D009713:Nucleotidyltransferases; C020658:glutamine-synthetase adenylyltransferase; C081173:glutamine synthetase I; D005974:Glutamate-Ammonia Ligase