Nucleic Acids Research Advance Access published online on August 25, 2006
Nucleic Acids Research, doi:10.1093/nar/gkl508
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© 2006 The Author(s)
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/2.0/uk/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
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Mechanisms of a ring shaped helicase
Department of Biochemistry, UMDNJ, Robert Wood Johnson Medical School 675 Hoes Lane, Piscataway, NJ 08854, USA
*To whom correspondence should be addressed. Tel: +1 732 235 3372; Fax: +1 732 235 4739; Email: patelss@umdnj.edu
Received April 1, 2006. Revised July 1, 2006. Accepted July 3, 2006.
Bacteriophage T7 helicase (T7 gene 4 helicase-primase) is a prototypical member of the ring-shaped family of helicases, whose structure and biochemical mechanisms have been studied in detail. T7 helicase assembles into a homohexameric ring that binds single-stranded DNA in its central channel. Using RecA-type nucleotide binding and sensing motifs, T7 helicase binds and hydrolyzes several NTPs, among which dTTP supports optimal protein assembly, DNA binding and unwinding activities. During translocation along single stranded DNA, the subunits of the ring go through dTTP hydrolysis cycles one at a time, and this probably occurs also during DNA unwinding. Interestingly, the unwinding speed of T7 helicase is an order of magnitude slower than its translocation rate along single stranded DNA. The slow unwinding rate is greatly stimulated when DNA synthesis by T7 DNA polymerase is coupled to DNA unwinding. Using the T7 helicase as an example, we highlight critical findings and discuss possible mechanisms of helicase action.
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