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  • The EMBO Journal (2008) 27, 1388 - 1398
  • doi:10.1038/emboj.2008.69

Published online: 3 April 2008

Motor step size and ATP coupling efficiency of the dsDNA translocase EcoR124IEMBO Open

Ralf Seidel1,2, Joost GP Bloom1, Cees Dekker1 and Mark D Szczelkun3

  1. Kavli Institute of Nanoscience, Delft University of Technology, Delft, The Netherlands
  2. DNA Motors Group, Biotechnological Centre, University of Technology Dresden, Dresden, Germany
  3. DNA–Protein Interactions Unit, Department of Biochemistry, University of Bristol, Bristol, UK

Correspondence to:

Cees Dekker, Kavli Institute of Nanoscience, Delft University of Technology, Lorentzweg 1, 2628 CJ Delft, The Netherlands. Tel.: +31 15 278 6094; Fax: +31 15 278 1202; E-mail: c.dekker@tudelft.nl

Mark D Szczelkun, DNA–Protein Interactions Unit, Department of Biochemistry, University of Bristol, Bristol BS8 1TD, UK. Tel.: +44 117 331 2158; Fax: +44 117 331 2168; E-mail: mark.szczelkun@bristol.ac.uk

Received 18 October 2007; Accepted 3 March 2008

The Type I restriction-modification enzyme EcoR124I is an archetypical helicase-based dsDNA translocase that moves unidirectionally along the 3'–5' strand of intact duplex DNA. Using a combination of ensemble and single-molecule measurements, we provide estimates of two physicochemical constants that are fundamental to a full description of motor protein activity—the ATP coupling efficiency (the number of ATP consumed per base pair) and the step size (the number of base pairs transported per motor step). Our data indicate that EcoR124I makes small steps along the DNA of 1 bp in length with 1 ATP consumed per step, but with some uncoupling of the ATPase and translocase cycles occurring so that the average number of ATP consumed per base pair slightly exceeds unity. Our observations form a framework for understanding energy coupling in a great many other motors that translocate along dsDNA rather than ssDNA.

  • Keywords:

    • ATPase,
    • helicase,
    • molecular motor,
    • single molecule,
    • stopped flow

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The EMBO Journal is published by Nature Publishing Group on behalf of European Molecular Biology Organization