Degradation of carboxy-terminal-tagged cytoplasmic proteins by the Escherichia coli protease HflB (FtsH)

  1. Christophe Herman,
  2. Danielle Thévenet,
  3. Philippe Bouloc,
  4. Graham C. Walker, and
  5. Richard D’Ari
  1. Université Libre de Bruxelles, B-1640 Rhode-Saint-Genèse, Belgium; Institut Jacques Monod [Centre National de la Recherche Scientifique (CNRS), Université Paris 6, Université Paris7], F-75251 Paris Cedex 05, France; Institut de Génétique et Microbiologie (Université Paris-Sud, CNRS), F-91405 Orsay Cedex, France; Department of Biology, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 USA

Abstract

Proteins with short nonpolar carboxyl termini are unstable inEscherichia coli. This proteolytic pathway is used to dispose of polypeptides synthesized from truncated mRNA molecules. Such proteins are tagged with an 11-amino-acid nonpolar destabilizing tail via a mechanism involving the 10Sa (SsrA) stable RNA and then degraded. We show here that the ATP-dependent zinc protease HflB (FtsH) is involved in the degradation of four unstable derivatives of the amino-terminal domain of the λcI repressor: three with nonpolar pentapeptide tails (cI104, cI105,cI108) and one with the SsrA tag (cI–SsrA). cI105 and cI-SsrA are also degraded by the ClpP-dependent proteases. Loss of ClpP can be compensated for by overproducing HflB. In an in vitro system,cI108 and cI–SsrA are degraded by HflB in an energy-dependent reaction, indicating that HflB itself recognizes the carboxyl terminus. These results establish a tail-specific pathway for removing abnormal cytoplasmic proteins via the HflB and Clp proteases.

Keywords

Footnotes

  • Corresponding author. Present address: Department of Stomatology, UCSF Medical Center, San Francisco, California 94143 USA.

  • E-MAIL lherman{at}itsa.ucsf.edu; FAX (415) 476-4204.

    • Received February 6, 1998.
    • Accepted March 12, 1998.
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