PERSISTENCE LENGTH OF RNA

A set of 10 double-stranded RNAs ranging in length from 92 to 317 base pairs has been synthesized, and their rotational diffusion times were measured by transient electric birefringence. A hydrodynamic analysis oi the birefringence decay data yields a helix persistence length of 720 +/- 70 Angstrom, based on a helix with an effective hydrodynamic d iameter of 26 Angstrom and a rise per base pair of 2.7 Angstrom in the presence of Mg2+ ions. Thus, duplex RNA is somewhat stiffer than DNA, for which the persistence length is 450-500 Angstrom. The measurement s also suggest that (i) current hydrodynamic theory for the rotational decay times is applicable to RNA molecules that are longer than 100 b ase pairs and (ii) weak Mg2+-RNA association decreases the rise per ba se pair slightly, by no more than 0.1 Angstrom.