Synthesis and properties of poly 5-methylthiouridylic acid

In an effort to search for good methods for the enzymatic synthesis of polynucleotide analogs with antitemplate activity, 5-methylthiouridine-5'-diphosphate (ms5UDP) has been synthesized and investigated as a substrate for polynucleotide phosphorylase. While ms5UDP was polymerized at a very low rate to give a 6% yield of polynucleotides by the polynucleotide phosphorylase of Micrococcus luteus, it was utilized more efficiently by the corresponding enzyme of Escherichia coli resulting in a 15% yield of poly (5-methylthiouridylic) acid. Results of the co-polymerization of ms5UDP and UDP revealed that the ratio of 5-methylthiouridylate to uridylate residues in the polynucleotide product was lower than the ratio of ms5UDP to UDP in the substrate mixture. The 5-methylthio group conferred only minute changes on the conformation of the modified polyuridylic acid, and the complexes formed between poly-(5-methylthiouridylic) acid and poly(adenylic) acid possessed slightly higher Tm values than did the unmodified counterparts. Poly(5-methylthiouridylic) acid was a potent inhibitor of calf thymus DNA polymerase alpha.