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Impediment of E. coli UvrD by DNA-destabilizing force reveals a strained-inchworm mechanism of DNA unwinding.
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- المؤلفون: Sun, Bo1; Wei, Kong-Ji1; Zhang, Bo2; Zhang, Xing-Hua1; Dou, Shuo-Xing1; Li, Ming1; Xi, Xu Guang2
- المصدر:
EMBO Journal. 12/24/2008, Vol. 27 Issue 24, p3279-3287. 9p. 1 Diagram, 1 Chart, 4 Graphs.
- الموضوع:
- معلومة اضافية
- نبذة مختصرة :
Escherichia coli UvrD is a non-ring-shaped model helicase, displaying a 3′–5′ polarity in DNA unwinding. Using a transverse magnetic tweezer and DNA hairpins, we measured the unwinding kinetics of UvrD at various DNA-destabilizing forces. The multiform patterns of unwinding bursts and the distributions of the off-times favour the mechanism that UvrD unwinds DNA as a dimer. The two subunits of the dimer coordinate to unwind DNA processively. They can jointly switch strands and translocate backwards on the other strand to allow slow (∼40 bp/s) rewinding, or unbind simultaneously to allow quick rehybridization. Partial dissociation of the dimer results in pauses in the middle of the unwinding or increases the translocation rate from ∼40 to ∼150 nt/s in the middle of the rewinding. Moreover, the unwinding rate was surprisingly found to decrease from ∼45 to ∼10 bp/s when the force is increased from 2 to 12 pN. The results lead to a strained-inchworm mechanism in which a conformational change that bends and tenses the ssDNA is required to activate the dimer. [ABSTRACT FROM AUTHOR]
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