Structural implications of electric-field induced dichroism of nucleic acids: Studies of alternating purine-pyrimidines.

ABSTRACT

Transient and steady-state electric dichroism measurements of double helical poly(dG-dC) and its 5-methyl guanosine analogue and transient electric dichroism measurements of double helical poly(dA-dT) are shown to give the following information on the structural and dynamical properties of these molecular systems (i) the Z form structure of the alternating guanosine-cytidine moieties has the same inter base-pair separation in solution as it does in the fibre and crystalline forms; (ii) the mean normal to the base pairs (and thus their average tilt and twist) of the B and Z forms of the guanosine-cytidine moieties is very nearly the same despite the large difference in their secondary structure; (iii) the alternating adenosinethymidine nucleic acid is at least twice as flexible as random-sequence DNA.