Nonenzymatic synthesis of oligoadenylates on a polyuridylic acid template.

Abstract

A number of nucleosides and mononucleotides have been shown to interact with complementary polynucleotides to form ordered helices of welldefined stoichiometry.1-3These latter are believed to have structures closely resembling those formed by corresponding pairs of polynucleotides.The condensation of preformed hexathymidylate residues to the dodecadeoxynucleotide in the presence of polyadenylic acid has already been reported.4We shall show that this reaction can be extended to the monomers adenosine and adenylic acid when they are incorporated in an ordered helix with poly U.Experimental and Results.-(a)Physical methods: Paper chromatography was carried out on Whatman 3 MM paper by the descending technique.The solvent systems were: I, isopropanol-concentrated ammonia-water (7:1:2, v/v); II, n-propanol-concentrated ammonia-water (55:10: 35, v/v); III, saturated aqueous ammonium sulphate-0.1 M sodium acetate-isopropanol (79:19:2, v/v); VIII, n-butanol-5 M acetic acid (2: 1, v/v).Thin-layer chromatography (system IV) was performed on Brinkmann MN-Polygram Cel 300 PEI, by the ascend- ing technique.5The sheets (20 X 20 cm) were prewashed with water and air- dried before application of substrate; they were developed for one hour in 0.5 M NaCl, then for two to three hours in 1.0 M NaCl.A paper wick applied to the upper edge allowed the solvent front to overrun.Paper electrophoresis was carried out on Whatman 3 MM paper, using varsol or CCl4 as coolant.The buf- fers were: V, potassium phosphate, 0.03 M, pH 7.1; VI, formic acid-ammonium formate, 0.05 M, pH 2.6; VII, sodium borate, 0.05 M, pH 9.0.-Chromatographic and electrophoretic data are collected in Tables 1 and2.Chromatograms and electrophoretograms of radioactive samples were cut into strips and passed through a Baird-Atomic RSC-363 scanner, to give a graphic record.Relevant areas were cut out and their radioactivities measured more precisely in a liquid scintillation system (Beckman LS-200).The papers were placed directly in Liquifluor diluted with toluene.(b) Materials: Poly U was obtained from Schwarz BioResearch.Before use, it was dialyzed against 0.5 M NaCl, then against distilled water, and finally lyophilized in order to yield the sodium salt, free of small molecules.The product was checked for oligomers in system II and found to contain none.Nucleo- sides and nucleotides, including those isotopically labeled, were supplied by Schwarz.