Effects of Poly(9-vinyladenine) and Poly(1-vinyluracil) on Messenger Ribonucleic Acid Template Activity

The neutral polynucleotide analogues poly(9-vinyladenine) and poly(1-vinyluracil) were found to inhibit [ 3 H]dTTP incorporation in a system containing rabbit hemoglobin mRNA as template, oligo( dT ) as primer, and purified avian myeloblastosis RNA-dependent DNA polymerase. The incorporation was inhibited 50% at an analogue concentration of 0.1 mM in base residues. Complexes of homopolynucleotides with vinyl polymers were tested as templates in a cell-free amino acid-incorporating system prepared from Krebs II ascites cells. Poly(9-vinyladenine) inhibited poly(U)-stimulated [ 14 C]phenylalanine incorporation, while poly(1-vinyluracil) inhibited poly(A)-stimulated [ 14 c]lysine incorporation. In neither case was the noncomplementary vinyl polymer inhibitory. Although poly(9-vinyladenine) had no effect on rabbit globin mRNA-stimulated amino acid incorporation in a cell-free system prepared from the Krebs II ascites tumor, poly(1-vinyluracil) was slightly inhibitory, with 50% inhibition occurring at a concentration of 10 mM uracil residues. However, similar inhibition occurred with a preparation of mRNA which did not contain the 3'-terminal poly(A) sequence, indicating that the inhibition occurring with high concentrations of poly(1-vinyluracil) does not involve the 3'-teminal poly(A) of the mRNA. The radioactive proteins produced in the cell-free system both with and without vinyl polymer coelectrophoresed with rabbit globin marker. These results suggest that the 3'-terminal poly(A) sequence of mRNA does not function in cell-free protein synthesis. Furthermore, the failure of the vinyl polymers to significantly inhibit cell-free protein synthesis suggests that the mechanism of vinyl polymer inhibition of murine leukemia virus replication in mouse cells involves inhibition of RNA-dependent DNA polymerase rather than inhibition of viral protein synthesis.