Inhibition of RNA-Dependent DNA Polymerase of Avian Myeloblastosis Virus by Pyran Copolymer (RNA tumor viruses/polymerase inhibitors)

Pyran copolymer, a known immunostimu- lator, was found to be a potent inhibitor of purified DNA polymerase (deoxynucleosidetriphosphate: DNA deoxynu- cleotidyltransferase; EC 2.7.7.7) isolated from avian myeloblastosis virus. Unlike other inhibitors, pyran showed unique features of inhibition. It interacts with the polymerase at a region other than the template site. The inhibitory effect was overcome only by excess enzyme and not affected by excess template. The degree of inhibition was not template specific for the templates tested: 70S RNA from avian myeloblastosis virus, synthetic hybrid poly(rA) oligo(dT)lo, synthetic copolymer poly(dA-dT), and activated calf-thymus DNA. The observed rate of in- hibition by pyran was shown to vary with the different polymerases tested. Inhibition was shown with all on- cornaviral polymerases and, to a lesser extent, with mammalian polymerases. However, two of the three bac- terial polymerases, by contrast, showed a marked activa- tion.