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Nucleic Acids Research Advance Access published online on September 26, 2009
Nucleic Acids Research, doi:10.1093/nar/gkp794
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© The Author(s) 2009. Published by Oxford University Press.
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/2.5/uk/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Nucleic Acid Enzymes

The single polypeptide restriction–modification enzyme LlaGI is a self-contained molecular motor that translocates DNA loops

Rachel M. Smith1, Jytte Josephsen2 and Mark D. Szczelkun1,*

1DNA–Protein Interactions Unit, Department of Biochemistry, School of Medical Sciences, University of Bristol, Bristol, BS8 1TD, UK and 2Department of Dairy and Food Science, Faculty of Life Sciences, University of Copenhagen, Rolighedsvej 30, DK-1958 Frederiksberg C, Denmark

*To whom correspondence should be addressed. Tel: +44 117 331 2158; Fax: +44 117 331 2168; Email: mark.szczelkun{at}bristol.ac.uk

Received July 28, 2009. Revised September 4, 2009. Accepted September 8, 2009.

To cleave DNA, the single polypeptide restriction–modification enzyme LlaGI must communicate between a pair of indirectly repeated recognition sites. We demonstrate that this communication occurs by a 1-dimensional route, namely unidirectional dsDNA loop translocation rightward of the specific recognition sequence 5'-CTnGAyG-3' as written (where n is either A, G, C or T and y is either C or T). Motion across thousands of base pairs is catalysed by the helicase domain and requires the hydrolysis of 1.5-2 ATP per base pair. DNA loop extrusion is accompanied by changes in DNA twist consistent with the motor following the helical pitch of the polynucleotide track. LlaGI is therefore an example of a polypeptide that is a completely self-contained, multi-functional molecular machine.

Present address: Jytte Josephsen, Øresund Food Network, Nørre Voldgade 16, DK 1358, Copenhagen K, Denmark


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