laboratoire de physique statistique
 
 
laboratoire de physique statistique

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882
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2007
DOI
881
Real-time observation of bacteriophage T4 gp41 helicase reveals an unwinding mechanism - Lionnet, Timothee and Spiering, Michelle M. and Benkovic, Stephen J. and Bensimon, David and Croquette, Vincent
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA 10419790-19795 (2007)

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 (approximate to 400 bp/s), its unwinding rate extrapolated to zero force is much slower (approximate to 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.
DOI
882
Developable modes in vibrated thin plates - Boudaoud, Arezki and Hamm, Eugenio and Melo, Francisco
PHYSICAL REVIEW LETTERS 99 (2007)

Abstract : We investigate the normal modes of a developable cone singularity as observed in a circular sheet supported by a rigid circular frame and pushed at its center. When the center of the sheet is in addition submitted to a sinusoidal forcing, two types of bending modes, named here rolling and tilt modes, are parametrically excited. The rolling mode is an angular oscillation of the concave sector of the developable cone structure. If the amplitude of vibration is high enough, the rolling mode amplitude increases dramatically giving rise to both a continuous rotation of the concave sector and a material angular displacement of the sheet, similar to that produced by a moving wrinkle in a carpet.