Site-directed mutagenesis of proteinase 3C results in a poliovirus deficient in synthesis of viral RNA polymerase

We used a synthetic double-stranded oligonucleotide to introduce amino acid substitutions into the proteinase 3C region of a poliovirus type 1 cDNA clone. The six different mutant viruses recovered exhibited a small-plaque phenotype when assayed on HeLa cells. Further investigation revealed that all the mutations (with the exception of one) yielded P3 region proteins that displayed altered mobility in sodium dodecyl sulfate-polyacrylamide gel electrophoresis. A conservative Val----Ala change at amino acid 54 of the proteinase resulted in a virus that was deficient in the production of the mature viral RNA polymerase 3D. Although this mutant achieved less than one-half of the wild-type levels of RNA synthesis during the course of infection, it still grew to nearly wild-type titers.