Polynucleotides. VI. Molecular properties and conformation of polyribouridylic acid

Optical, hydrodynamic, and titration properties of polyribouridylic acid (poly U) were investigated in 0.2 M Na + , pH 6. Above 15°C., poly U was shown to be a randomly coiled single chain, devoid of secondary structure. There is no shear rate dependence of viscosity; molecular weight is independent of ionic strength; there is virtually no conformationally dependent hypochromicity; no anomalous optical rotatory dispersion; and no anomalous titration behavior. The dependence of the sedimentation constant and intrinsic viscosity on molecular weight was determined. Poly U was shown to be the most highly expanded of all synthetic and naturally occurring randomly coiled polynucleotides.