Influence of a Mechanical Tension on the B-C and B-C Conformational Transitions in DNA Fibres

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Abstract
In the present fibre X-ray study we attempt to quantify the effect of a mechanical tension on the conformations, and transitions between the structural forms of DNA A simple experimental device has been realized in order to apply precise mechanical forces on DNA fibres during X-ray exposure. It is shown that, as the applied tension is increased, the B→A transition can be prevented as well as with a decrease of the sodium salt content A kind of distorted B form is then observed the helical parameters of which change with the relative humidity. On the contrary, the mechanical tension does not prevent the B→C transition; it only slows down the form change and improves the X-ray patterns up to a relative humidity of 0%.