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  • The EMBO Journal (2009) 28, 1732 - 1744
  • doi:10.1038/emboj.2009.134

Published online: 14 May 2009

Modification of PATase by L/F-transferase generates a ClpS-dependent N-end rule substrate in Escherichia coli

Robert L Ninnis1, Sukhdeep K Spall1, Gert H Talbo1, Kaye N Truscott1 and David A Dougan1

  1. Department of Biochemistry, La Trobe University, Melbourne, Victoria, Australia

Correspondence to:

David A Dougan, Department of Biochemistry, La Trobe University, Kingsbury Drive, Melbourne, Victoria 3086, Australia. Tel.: +61 3 9479 3276; Fax: +61 3 9479 2467; E-mail: d.dougan@latrobe.edu.au

Kaye N Truscott, Department of Biochemistry, La Trobe University, Kingsbury Drive, Melbourne, Victoria 3086, Australia. Tel.: +61 3 9479 3276; Fax: +61 3 9479 2467; E-mail: k.truscott@latrobe.edu.au

Received 13 October 2008; Accepted 22 April 2009

The N-end rule pathway is conserved from bacteria to man and determines the half-life of a protein based on its N-terminal amino acid. In Escherichia coli, model substrates bearing an N-degron are recognised by ClpS and degraded by ClpAP in an ATP-dependent manner. Here, we report the isolation of 23 ClpS-interacting proteins from E. coli. Our data show that at least one of these interacting proteins—putrescine aminotransferase (PATase)—is post-translationally modified to generate a primary N-degron. Remarkably, the N-terminal modification of PATase is generated by a new specificity of leucyl/phenylalanyl-tRNA-protein transferase (LFTR), in which various combinations of primary destabilising residues (Leu and Phe) are attached to the N-terminal Met. This modification (of PATase), by LFTR, is essential not only for its recognition by ClpS, but also determines the stability of the protein in vivo. Thus, the N-end rule pathway, through the ClpAPS-mediated turnover of PATase may have an important function in putrescine homeostasis. In addition, we have identified a new element within the N-degron, which is required for substrate delivery to ClpA.

  • Keywords:

    • ClpS,
    • LFTR,
    • N-degron,
    • N-end rule pathway,
    • substrate binding