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PicoNewton-millisecond force steps reveal the transition kinetics and mechanism of the double-stranded DNA elongation.

ABSTRACT: We study the kinetics of the overstretching transition in ?-phage double-stranded (ds) DNA from the basic conformation (B state) to the 1.7-times longer and partially unwound conformation (S state), using the dual-laser optical tweezers under force-clamp conditions at 25°C. The unprecedented resolution of our piezo servo-system, which can impose millisecond force steps of 0.5-2 pN, reveals the exponential character of the elongation kinetics and allows us to test the two-state nature of the B-S transition mechanism. By analyzing the load-dependence of the rate constant of the elongation, we find that the elementary elongation step is 5.85 nm, indicating a cooperativity of ~25 basepairs. This mechanism increases the free energy for the elementary reaction to ~94 k(B)T, accounting for the stability of the basic conformation of DNA, and explains why ds-DNA can remain in equilibrium as it overstretches.

SUBMITTER: Bianco P

PROVIDER: S-EPMC3175059 | biostudies-literature | 2011 Aug

REPOSITORIES: biostudies-literature

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PicoNewton-millisecond force steps reveal the transition kinetics and mechanism of the double-stranded DNA elongation.

Bianco Pasquale P Bongini Lorenzo L Melli Luca L Dolfi Mario M Lombardi Vincenzo V

Biophysical journal 20110801 4

We study the kinetics of the overstretching transition in λ-phage double-stranded (ds) DNA from the basic conformation (B state) to the 1.7-times longer and partially unwound conformation (S state), using the dual-laser optical tweezers under force-clamp conditions at 25°C. The unprecedented resolution of our piezo servo-system, which can impose millisecond force steps of 0.5-2 pN, reveals the exponential character of the elongation kinetics and allows us to test the two-state nature of the B-S ...[more]

PMID: 21843477

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