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Condensation prevails over B-A transition in the structure of DNA at low humidity.

ABSTRACT: B-A transition and DNA condensation are processes regulated by base sequence and water activity. The constraints imposed by interhelical interactions in condensation compromise the observation of the mechanism by which B and A base-stacking modes influence the global state of the molecule. We used a single-molecule approach to prevent aggregation and mechanical force to control the intramolecular chain association involved in condensation. Force-extension experiments with optical tweezers revealed that DNA stretches as B-DNA under ethanol and spermine concentrations that favor the A-form. Moreover, we found no contour-length change compatible with a cooperative transition between the A and B forms within the intrinsic-force regime. Experiments performed at constant force in the entropic-force regime with magnetic tweezers similarly did not show a bistable contraction of the molecules that could be attributed to the B-A transition when the physiological buffer was replaced by a water-ethanol mixture. A total, stepwise collapse was found instead, which is characteristic of DNA condensation. Therefore, a low-humidity-induced change from the B- to the A-form base-stacking alone does not lead to a contour-length shortening. These results support a mechanism for the B-A transition in which low-humidity conditions locally change the base-stacking arrangement and globally induce DNA condensation, an effect that may eventually stabilize a molecular contour-length reduction.

SUBMITTER: Hormeno S

PROVIDER: S-EPMC3077702 | biostudies-literature | 2011 Apr

REPOSITORIES: biostudies-literature

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Condensation prevails over B-A transition in the structure of DNA at low humidity.

Hormeño Silvia S Moreno-Herrero Fernando F Ibarra Borja B Carrascosa José L JL Valpuesta José M JM Arias-Gonzalez J Ricardo JR

Biophysical journal 20110401 8

B-A transition and DNA condensation are processes regulated by base sequence and water activity. The constraints imposed by interhelical interactions in condensation compromise the observation of the mechanism by which B and A base-stacking modes influence the global state of the molecule. We used a single-molecule approach to prevent aggregation and mechanical force to control the intramolecular chain association involved in condensation. Force-extension experiments with optical tweezers reveal ...[more]

PMID: 21504737

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Condensation prevails over B-A transition in the structure of DNA at low humidity.

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Condensation prevails over B-A transition in the structure of DNA at low humidity.

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