We have investigated the elastic properties of poly(U), homopolymeric single-stranded RNA molecules that lack any base pairing and stacking interactions and conform to a random-coil structure. Using single-molecule stretching experiments we show that the elastic properties are described by a wormlike chain model for polymer elasticity rather than by a freely jointed chain model as is commonly used for single-stranded DNA. At low [${\mathrm{N}\mathrm{a}}^{+}$], introduction of a scale-dependent persistence length is required to account for electrostatic contributions.

• Received 8 December 2003

DOI:https://doi.org/10.1103/PhysRevLett.93.118102