Structure of strand-separted DNA in different environments studied by linear dichroism

We have studied the denaturation of DNA by linear dichroism (LD) techniques in the following systems: (1) in aqueous solution at low pH, (2) in 90% (w/w) ethylene glycol and in 90% glycerol solutions, and (3) in a matrix of polyvinyl alcohol (PVA). We report that denatured DNA at low ionic strength can be oriented by shear forces in all these systems and that it exhibits positive LD with markedly varying LD/A over the absorption band centered at 260 nm (A being the ordinary absorbance) as compared to the negative LD with approximately constant LD/A of ordinary native DNA. These results are interpreted in terms of a large tilt of the planes of the DNA bases. DNA adopts denatured forms in (1) aqueous solutions at p