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Proc Natl Acad Sci U S A. 2007 Dec 11;104(50):19790-5. Epub 2007 Dec 5.

Real-time observation of bacteriophage T4 gp41 helicase reveals an unwinding mechanism.

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1
Laboratoire de Physique Statistique, Ecole Normale Supérieure, Centre National de la Recherche Scientifique-UMR8550, 24 Rue Lhomond, 75005 Paris, France. tlionnet@aecom.yu.edu

Abstract

Helicases are enzymes that couple ATP hydrolysis to the unwinding of double-stranded (ds) nucleic acids. The bacteriophage T4 helicase (gp41) is a hexameric helicase that promotes DNA replication within a highly coordinated protein complex termed the replisome. Despite recent progress, the gp41 unwinding mechanism and regulatory interactions within the replisome remain unclear. Here we use a single tethered DNA hairpin as a real-time reporter of gp41-mediated dsDNA unwinding and single-stranded (ss) DNA translocation with 3-base pair (bp) resolution. Although gp41 translocates on ssDNA as fast as the in vivo replication fork ( approximately 400 bp/s), its unwinding rate extrapolated to zero force is much slower ( approximately 30 bp/s). Together, our results have two implications: first, gp41 unwinds DNA through a passive mechanism; second, this weak helicase cannot efficiently unwind the T4 genome alone. Our results suggest that important regulations occur within the replisome to achieve rapid and processive replication.

PMID:
18077411
PMCID:
PMC2148377
DOI:
10.1073/pnas.0709793104
[Indexed for MEDLINE]
Free PMC Article
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