DETERMINATION OF THE POLIOVIRUS RNA-POLYMERASE ERROR FREQUENCY AT 8 SITES IN THE VIRAL GENOME

The poliovirus RNA polymerase error frequency was measured in vivo at eight sites in the poliovirus genome. The frequency at which specific G residues in poliovirion RNA changed to another base during one round of viral RNA replication was determined. Poliovirion RNA uniformly labeled with P-32i was hybridized to a synthetic DNA oligonucleotide that was complementary to a sequence in the viral genome that contained a single internal G residue. The nonhybridized viral RNA was digested with RNase T1, and the protected RNA oligonucleotide was purified by gel electrophoresis. The base substitution frequency at the internal G residue was measured by finding the fraction of this RNA oligonucleotide that was resistant to RNase T1 digestion. A mean value of 2.0 x 10(-3) +/- 1.2 x 10(-3) was obtained at two sites. A modification of the above procedure involved the use of 5'-end-labeled RNA oligonucleotides. The mean value of the error frequency determined at eight sites in the viral genome by using this technique was 4.1 x 10(-3) +/- 0.6 x 10(-3). Sequencing two of the RNase T1-resistant RNA oligonucleotides confirmed that the internal G was changed to a C, A, or U residue in most of these oligonucleotides. Thus, our results indicated that the polymerase had a high error frequency in vivo and that there was no significant variation in the values determined at the specific sites examined in this study.