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An alternative P II protein in the regulation of glutamine synthetase in Escherichia coli
Author(s) -
Van Heeswijk Wally C.,
Hoving Sjouke,
Molenaar Douwe,
Stegeman Brenda,
Kahn Daniel,
Westerhoff Hans V.
Publication year - 1996
Publication title -
molecular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 247
eISSN - 1365-2958
pISSN - 0950-382X
DOI - 10.1046/j.1365-2958.1996.6281349.x
Subject(s) - biology , glutamine synthetase , biochemistry , adenylylation , glutamine , operon , escherichia coli , sigma factor , nitrogen assimilation , amino acid , gene , microbiology and biotechnology , rna polymerase , biosynthesis
The P II protein has been considered pivotal to the dual cascade regulating ammonia assimilation through glutamine synthetase activity. Here we show that P II , 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 P II and a putative ammonia transporter. We cloned and overexpressed glnK and found that the expressed protein had almost the same molecular weight as P II , reacted with polyclonal P II antibody, and was 67% identical in terms of amino acid sequence with Escherichia coli P II . Like P II , 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 P II , 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 σ N (σ 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 P II . Possible regulatory implications of this conditional redundancy of P II are discussed.