Figure 4.

(A) Specific infectivity of T7 transcribed poliovirus genomes compared with natural poliovirus genomes. This illustrates that between 0.21 and 2.1 mutations per 10,000 nt (Table 1), there is no significant detrimental effect on the viability (specific infectivity) of poliovirus genomes. In vitro-transcribed RNA (■); natural poliovirus RNA (●). Average data set is shown. (B) Relationship of mutation frequency to genomic RNA infectivity. Specific infectivity of normal poliovirus RNA was set to 100%. The graph shows that poliovirus populations exist near the edge of error catastrophe, as there is a rapid decline in RNA genome infectivity at levels of mutagenesis only slightly higher than normal. The LI₅₀ (50% loss of specific infectivity) is defined as the mutation frequency at which 50% of the viral genomes are lethally mutated, indicated by the dashed line. Wild-type (wt or Mo) poliovirus genomes contain an average ≈1.5 mutations/genome, based on data from Table 1. Poliovirus genomes from cells treated with 100 μM ribavirin (Table 3) contain an average ≈1.9 mutations/genome. Poliovirus genomes from cells treated with 400 μM ribavirin (Table 3) contain an average ≈6.9 mutations/genome. Poliovirus genomes from cells treated with 1,000 μM ribavirin (Table 3) contain an average ≈15.5 mutations/genome.