The inhibition of polynucleotide phosphorylase by specific polymers.

Mii and Ochoa (7) discovered that the synthesis of certain homopolymers by polynucleotide phosphorylase is stimulated by the corresponding polynucleotides or by various copolymers, as well as by ribonucleic acid. These results were confirmed by Singer, Heppel, and Hilmoe (8, 9), who also showed that oligonucleotides are good primers for polynucleotide synthesis. In addition to these stimulations, a curious inhibition reaction was reported from Ochoa’s laboratory (7, 10). The polymerization of ADP is inhibited by poly U,2 and the polymerization of UDP is inhibited by poly A. It was shown later by Singer, Hilmoe, and Grunberg-Manago (4) that the same relationships hold when the nucleoside diphosphate-Pi32 “exchange” is studied. The present communication is concerned with these inhibition reactions. We shall refer to them as specific polymer inhibitions for the following reason. A nearly complete survey of every combination of nucleoside diphosphate and homopolymer shows that inhibition of polymerization or of the nucleoside diphosphate-Pi32 incorporation reaction occurs only in the presence of specific polymers. It is required that the inhibiting polymer and the nucleoside diphosphate furnish a pair of bases that are different from one another but able to form strong hydrogen bonds. For example, polymerization of ADP is inhibited by poly U and poly I, but not by poly C or poly G. This can be correlated with the fact that poly A forms hydrogen-bonded complexes with poly