Details

Autor(en) / Beteiligte

• Hormeño, Silvia
• Moreno-Herrero, Fernando
• Ibarra, Borja
• Carrascosa, José L.
• Valpuesta, José M.
• Arias-Gonzalez, J. Ricardo

Titel

Condensation Prevails over B-A Transition in the Structure of DNA at Low Humidity

Ist Teil von

• Biophysical journal, 2011-04, Vol.100 (8), p.2006-2015

Ort / Verlag

United States: Elsevier Inc

Erscheinungsjahr

2011

Link zum Volltext

Quelle

MEDLINE

Beschreibungen/Notizen

• 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.