Force-induced structural transitions in cross-linked DNA films

Abstract

We report on the preparation and characterization of wet-spun films of sodium DNA in which intermolecular cross-links were introduced following formaldehyde treatment. Raman scattering shows that the DNA in moderately cross-linked films is mainly in the B conformation. Stretching experiments show a transition from plastic to elastomeric behavior with increasing exposure to the cross-linking agent. Elastomeric DNA films are strongly disordered. X-ray diffraction shows that stretching of moderately cross-linked films under controlled high humidity conditions results in increased molecular orientation as well as the appearance of meridional reflections at 7.4-7.8 and 8.2 angstroms. These reflections are not observed for any of the classical conformations associated with mixed sequence DNA, and may arise from extended base-pair stacking in a stretched DNA structure.

Deforming DNA: From Physics to Biology

“…We remark that intercalation-like gaps of a similar width (8 ) have also been observed following a result of force-induced transition in cross-linked DNA films. [47] This feature, which is not seen in DNA molecules stretched by less or more than 50 %, is linked to base-pair inclination, which passes from negative in relaxed or weakly stretched DNA to positive in the strongly stretched state. Base-pair inclination allows stacking to be preserved during stretching, but at 50 % extension, the inclination is close to zero and, consequently, the observed disproportionation in stacking is the only route to improving stability.…”

DNA partitions into triplets under tension in the presence of organic cations, with sequence evolutionary age predicting the stability of the triplet phase

“…Molecular combing results show that DNA in its stretched form is not denatured, with a double-helix structure which is characterised by a diameter of 1·2 nm (Maaloum et al 2011). X-ray diffraction of stretched cross-linked films of a mixed sequence of DNA show gaps of ~8 Å (André et al 2008), nearly the same size as seen in the DNA–RecA complex. These experimental results suggest the existence of a stretched form of solution DNA with preserved base-pair stacking.…”