Torsional dynamics and rigidity of fractionated poly(dGdC).

Abstract

AbstractTime‐resolved fluorescence polarization anisotropy measurements were performed on two fractionated samples of duplex poly(dGdC) containing 230 (+40, −30) base pairs (bp) and 590 ± 40 bp. Deconvolution using the intermediate zone formula for the twisting correlation functions (which is not valid for such short DNAs) yields apparent torsion constants for these two samples that are disparate and, in any case, too low. By similarly deconvoluting simulated data constructed from the correct twisting correlation functions, it can be inferred that these two samples actually exhibit the same torsion constant, α = (4.0 ± 0.4) × 10−12 dyn cm. Within the experimental uncertainties, this value is the same as that reported previously from this laboratory for linear ϕ29 and linearized M13mp7 DNAs. The 590‐bp sample exhibited a peculiar evolution of its apparent torsional rigidity from a very high initial value, \documentclass{article}\pagestyle{empty}\begin{document}$ \hat \alpha $\end{document} = (11 ± 1) × 10−12 dyn cm, to a normal value over a period of several months, during which time many very small fragments appeared to be dissociated from, or annealed out, of the predominant high‐molecular‐weight species. Possible interpretations of these observations are discussed.