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Inorganic polyphosphate kinase is required to stimulate protein degradation and for adaptation to amino acid starvation in Escherichia coli.

Abstract
Inorganic polyphosphate (polyP) kinase was studied for its roles in physiological responses to nutritional deprivation in Escherichia coli. A mutant lacking polyP kinase exhibited an extended lag phase of growth, when shifted from a rich to a minimal medium (nutritional downshift). Supplementation of amino acids to the minimal medium abolished the extended growth lag of the mutant. Levels of the stringent response factor, guanosine 5'-diphosphate 3'-diphosphate, increased in response to the nutritional downshift, but, unlike in the wild type, the levels were sustained in the mutant. These results suggested that the mutant was impaired in the induction of amino acid biosynthetic enzymes. The expression of an amino acid biosynthetic gene, hisG, was examined by using a transcriptional lacZ fusion. Although the mutant did not express the fusion in response to the nutritional downshift, Northern blot analysis revealed a significant increase of hisG-lacZ mRNA. Amino acids generated by intracellular protein degradation are very important for the synthesis of enzymes at the onset of starvation. In the wild type, the rate of protein degradation increased in response to the nutritional downshift whereas it did not in the mutant. Supplementation of amino acids at low concentrations to the minimal medium enabled the mutant to express the hisG-lacZ fusion. Thus, the impaired regulation of protein degradation results in the adaptation defect, suggesting that polyP kinase is required to stimulate protein degradation.
AuthorsA Kuroda, S Tanaka, T Ikeda, J Kato, N Takiguchi, H Ohtake
JournalProceedings of the National Academy of Sciences of the United States of America (Proc Natl Acad Sci U S A) Vol. 96 Issue 25 Pg. 14264-9 (Dec 07 1999) ISSN: 0027-8424 [Print] United States
PMID10588694 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)
Chemical References
  • Amino Acids
  • Bacterial Proteins
  • Phosphotransferases (Phosphate Group Acceptor)
  • polyphosphate kinase
  • Ligases
  • guanosine 3',5'-polyphosphate synthetases
Topics
  • Adaptation, Physiological
  • Amino Acids (biosynthesis)
  • Bacterial Proteins (metabolism)
  • Escherichia coli (metabolism)
  • Ligases (physiology)
  • Phosphotransferases (Phosphate Group Acceptor) (physiology)

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