PicoNewton-millisecond force steps reveal the transition kinetics and mechanism of the double-stranded DNA elongation.
Biophys J
; 101(4): 866-74, 2011 Aug 17.
Article
em En
| MEDLINE
| ID: mdl-21843477
ABSTRACT
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 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.
Texto completo:
1
Coleções:
01-internacional
Base de dados:
MEDLINE
Assunto principal:
DNA
/
DNA Viral
/
Bacteriófago lambda
Tipo de estudo:
Prognostic_studies
Idioma:
En
Revista:
Biophys J
Ano de publicação:
2011
Tipo de documento:
Article
País de afiliação:
Itália