Persistence Length Changes Dramatically as RNA Folds

Abstract

We determine the persistence length, $l_p$, for a bacterial group I ribozyme as a function of concentration of monovalent and divalent cations by fitting the distance distribution functions $P(r)$ obtained from small angle X-ray scattering intensity data to the asymptotic form of the calculated $P_{WLC}(r)$ for a worm-like chain (WLC). The $l_p$ values change dramatically over a narrow range of \Mg concentration from $\sim$21 Åin the unfolded state (\textbf{U}) to $\sim$10 Åin the compact (${\mathrm{I}}_{\mathrm{C}}$) and native states. Variations in $l_p$ with increasing \Na concentration are more gradual. In accord with the predictions of polyelectrolyte theory we find $l_p\propto 1/{\kappa }^2$ where $\kappa$ is the inverse Debye-screening length.

4 page. Phys. Rev. Lett. in press