| Abstract: | The effect on viral replication of deleting nucleotide 10 of the poliovirus RNA genome was determined. This deletion, which removes a base pair from a predicted hairpin structure in the viral RNA, was introduced into full-length cDNA. Virus recovered after transfection of HeLa cells with the mutated cDNA contained the expected deletion and was temperature sensitive for plaque formation. Analysis of viral replication by one-step growth experiments indicated that mutant virus production at the nonpermissive temperature was at least 100 times less than that of wild type virus, and release of virus from mutant-infected cells was delayed. The synthesis of positive- and negative-strand viral RNA in mutant virus-infected cells was temperature sensitive. Virus-specific protein synthesis in mutant virus-infected cells was not temperature sensitive but occurred at a slower rate than that of wild type virus at permissive and nonpermissive temperatures. Replication of the mutant virus was sensitive to actinomycin D, in contrast to the wild type parent virus, which was resistant to the drug. Mutant virus stocks contained a small percentage of ts+ viruses that were able to form plaques at the nonpermissive temperature. Nucleotide sequence analysis of genomic RNA from these ts+ viruses revealed a single base change at position 34 from a G to U. In the positive RNA strand, the effect of this mutation is to restore to the hairpin structure the single base pair whose formation was prevented by the original deletion. The ts+ pseudorevertants replicated to similar titers as wild type virus at 33 and 38.5 degrees and were partially sensitive to actinomycin D. |
