Reversible uridylylation of the Escherichia coli PII signal transduction protein regulates its ability to stimulate the dephosphorylation of the transcription factor nitrogen regulator I (NRI or NtrC).
We have reconstituted the signal transduction system responsible for the negative regulation of the transcription of the Escherichia coli glnA gene, encoding glutamine synthetase, by glutamine. This signal transduction system consists of four proteins: the transcription factor NRI (NtrC), which activates glnA transcription when it is phosphorylated, the kinase/phosphatase protein NRII (NtrB) that directly controls the extent of NRI phosphorylation, the PII signal transduction protein that controls the phosphatase activity of NRII, and the uridylyltransferase/uridylyl-removing (UTase/UR) enzyme that is regulated by glutamine and controls the activity of PII. In the reconstituted system, the removal of uridylyl groups from the PII protein, catalyzed by the UTase/UR protein in the presence of glutamine, resulted in the stimulation of NRI approximately P dephosphorylation. In contrast, the uridylylated form of the PII protein had no discernible effect on NRI phosphorylation. The uridylylation of the trimeric PII protein by the monomeric UTase/UR protein is a non-cooperative reaction in which the partially modified species accumulated and were readily observed. Partially modified PII trimers were partially active in stimulating the dephosphorylation of NRI approximately P. Thus, both the PII-UTase/UR and PII-NRII interactions display the continuous variability characteristic of rheostats as opposed to the binary variability characteristic of toggle switches.
Department of Biological Chemistry, University of Michigan Medical School, Ann Arbor 48109-0606.
M R
MR
Atkinson
E S
ES
Kamberov
R L
RL
Weiss
A J
AJ
Ninfa
D001426:Bacterial Proteins; D004268:DNA-Binding Proteins / Q000302:isolation & purification / Q000378:metabolism*; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism*; D029968:Escherichia coli Proteins; D015964:Gene Expression Regulation, Bacterial / Q000187:drug effects; D005798:Genes, Bacterial; D005974:Glutamate-Ammonia Ligase / Q000096:biosynthesis* / Q000235:genetics; D005973:Glutamine / Q000494:pharmacology; D007700:Kinetics; D008954:Models, Biological; D009713:Nucleotidyltransferases / Q000302:isolation & purification / Q000378:metabolism*; D051922:PII Nitrogen Regulatory Proteins; D010749:Phosphoprotein Phosphatases / Q000302:isolation & purification / Q000378:metabolism*; D010766:Phosphorylation; D011494:Protein Kinases / Q000302:isolation & purification / Q000378:metabolism*; D015398:Signal Transduction; D013997:Time Factors; D015534:Trans-Activators; D014157:Transcription Factors; D014158:Transcription, Genetic
D001426:Bacterial Proteins; D004268:DNA-Binding Proteins; D029968:Escherichia coli Proteins; D051922:PII Nitrogen Regulatory Proteins; D015534:Trans-Activators; D014157:Transcription Factors; C497876:glnG protein, E coli; D005973:Glutamine; D011494:Protein Kinases; C055699:protein kinase-phosphatase NTRB; D009713:Nucleotidyltransferases; C022515:regulatory protein uridylyltransferase; D010749:Phosphoprotein Phosphatases; D005974:Glutamate-Ammonia Ligase