Double-stranded RNA resists condensation.

Much attention has been focused on DNA condensation because of its fundamental biological importance. The recent discovery of new roles for RNA duplexes demands efficient packaging of double-stranded RNA for therapeutics. Here we report measurements of short DNA and RNA duplexes in the presence of trivalent ions. Under conditions where UV spectroscopy indicates condensation of DNA duplexes into (insoluble) precipitates, RNA duplexes remain soluble. Small angle x-ray scattering results suggest that the differing surface topologies of RNA and DNA may be crucial in generating the attractive forces that result in precipitation.