title: An alternative PII protein in the regulation of glutamine synthetase in Escherichia coli.
abstract: The PII protein has been considered pivotal to the dual cascade regulating ammonia assimilation through glutamine synthetase activity. Here we show that PII, encoded by the glnB gene, is not always essential; for instance upon ammonia deprivation of a glnB deletion strain, glutamine synthetase can be deadenylylated as effectively as in the wild-type strain. We describe a new operon, glnK amtB, which encodes a homologue of PII and a putative ammonia transporter. We cloned and overexpressed glnK and found that the expressed protein had almost the same molecular weight as PII, reacted with polyclonal PII antibody, and was 67% identical in terms of amino acid sequence with Escherichia coli PII. Like PII, purified GlnK can activate the adenylylation of glutamine synthetase in vitro, and, in vivo, the GlnK protein is uridylylated in a glnD-dependent fashion. Unlike PII, however, the expression of glnK depends on the presence of UTase, nitrogen regulator I (NRI), and absence of ammonia. Because of a NRI and a sigma N (sigma 54) RNA polymerase-binding consensus sequence upstream from the glnK gene, this suggests that glnK is regulated through the NRI/NRII two-component regulatory system. Indeed, in cells grown in the presence of ammonia, glutamine synthetase deadenylylation upon ammonia depletion depended on PII. Possible regulatory implications of this conditional redundancy of PII are discussed.
authors.affiliation: E.C. Slater Institute, University of Amsterdam, The Netherlands.
authors.forename: W C
authors.initials: WC
authors.lastname: van Heeswijk
authors.forename: S
authors.initials: S
authors.lastname: Hoving
authors.forename: D
authors.initials: D
authors.lastname: Molenaar
authors.forename: B
authors.initials: B
authors.lastname: Stegeman
authors.forename: D
authors.initials: D
authors.lastname: Kahn
authors.forename: H V
authors.initials: HV
authors.lastname: Westerhoff
mesh_terms: D000595:Amino Acid Sequence; D000641:Ammonia / Q000378:metabolism; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D001483:Base Sequence; D001693:Biological Transport, Active / Q000235:genetics; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism; D002874:Chromosome Mapping; D003001:Cloning, Molecular; D004269:DNA, Bacterial / Q000235:genetics; D004926:Escherichia coli / Q000201:enzymology / Q000235:genetics / Q000378:metabolism*; D015964:Gene Expression Regulation, Bacterial; D005798:Genes, Bacterial; D005809:Genes, Regulator; D005974:Glutamate-Ammonia Ligase / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D009584:Nitrogen / Q000378:metabolism; D051922:PII Nitrogen Regulatory Proteins; D017386:Sequence Homology, Amino Acid
chemical_list: D001426:Bacterial Proteins; D002352:Carrier Proteins; D004269:DNA, Bacterial; D051922:PII Nitrogen Regulatory Proteins; C404143:PIID regulatory protein, Bacteria; D000641:Ammonia; D005974:Glutamate-Ammonia Ligase; D009584:Nitrogen