[Experimental method for studying conformational transitions in DNA].

An experimental method combining fiber X-ray and direct fiber dimension measurements is proposed for the study of DNA conformational transitions. Curves corresponding to the A-B and B-C transitions are obtained by using the proportionality which exists between the fiber length and the axial rise per nucleotide in the DNA helix. The A-B transition is shown to be cooperative while the B-C one is a progressive change of helical conformation.