Polyphosphate kinase is a component of the Escherichia coli RNA degradosome

Authors

  • Erwin Blum,

    1. Nuffield Department of Clinical Biochemistry and Imperial Cancer Research Fund Laboratories, Institute of Molecular Medicine, John Radcliffe Hospital, University of Oxford, Oxford OX3 9DS, UK.,
    Search for more papers by this author
  • Beatrice Py,

    1. Nuffield Department of Clinical Biochemistry and Imperial Cancer Research Fund Laboratories, Institute of Molecular Medicine, John Radcliffe Hospital, University of Oxford, Oxford OX3 9DS, UK.,
    Search for more papers by this author
    • Present address: Laboratoire de Chimie Bactérienne, Centre National de la Recherche Scientifique, 31 Chemin Joseph Aiguier, 13402 Marseille Cedex 20, France

  • Agamemnon J. Carpousis,

    1. Laboratoire de Microbiologie et Génétique Moléculaire du Centre National de la Recherche Scientifique, 118 Route de Narbonne, 31062 Toulouse, France.
    Search for more papers by this author
  • Christopher F. Higgins

    1. Nuffield Department of Clinical Biochemistry and Imperial Cancer Research Fund Laboratories, Institute of Molecular Medicine, John Radcliffe Hospital, University of Oxford, Oxford OX3 9DS, UK.,
    Search for more papers by this author

Christopher F. Higgins E-mail C.Higgins@icrf.icnet.uk; Tel. (01865) 222423; Fax (01865) 222431.

Abstract

The Escherichia coli degradosome is a multienzyme complex with four major protein components: the endoribonuclease RNase E, the exoribonuclease PNPase, the RNA helicase RhlB and enolase. The first three of these proteins are known to have important functions in mRNA processing and degradation. In this work, we identify an additional component of the degradosome, polyphosphate kinase (PPK), which catalyses the reversible polymerization of the γ-phosphate of ATP into polyphosphate (poly(P)). An E. coli strain deleted for the ppk gene showed increased stability of the ompA mRNA. Purified His-tagged PPK was shown to bind RNA, and RNA binding was prevented by hydrolysable ATP. Chemical modification of RNA by PPK, for example the addition or removal of 3′ or 5′ terminal phosphates, could not be detected. However, polyphosphate was found to inhibit RNA degradation by the degradosome in vitro. This inhibition was overcome by the addition of ADP, required for the degradation of polyphosphate and for the regeneration of ATP by PPK in the degradosome. Thus, PPK in the degradosome appears to maintain an appropriate microenvironment, removing inhibitory polyphosphate and NDPs and regenerating ATP.

Footnotes

  1. Present address: Laboratoire de Chimie Bactérienne, Centre National de la Recherche Scientifique, 31 Chemin Joseph Aiguier, 13402 Marseille Cedex 20, France

Ancillary