III. INTERACTION AND ULTRAVIOLET ABSORPTION

The discovery of polynucleotide phosphorylase has led to the availability of several types of polymers of ribonucleotides. Polymers of adenylic, uridylic, cytidylic, and inosinic acids’ and several of the possible copolymers have been prepared (2). Structure studies (3, 4) have shown that the nucleotides are linked by 3’, 5’ diester phosphate bonds and that the polymers are thus similar to ribonucleic acid. Because of this similarity and because of the simplification of structure which results from the presence of a single kind of nucleotide in the polymer chain, there are problems in nucleic acid structure and physical properties that may be illuminated by a study of the biosynthetic polymers. This paper deals with the spontaneous interaction between poly A’ and poly U with the formation of stable aggregates, as well as with certain features of the ultraviolet absorption spectra of these and other polymers bearing on the problem of polynucleotide interaction. Methods The polymers used in this work were prepared as previously described (2),2 having been furnished in the form of lyophilixed sodium salts, free from additional electrolyte. They were dissolved in water and diluted with various buffers as required. Electrophoresis was carried out at 0” as previously described (5). Sedimentation coefficients were determined with a Spinco model E ultracentrifuge at 16-20”. Diffusion coefficient,s were measured in a Gouy diffusiometer at 5’, this instrument having been made from a Pearson elec