Panels A–E: Incorporation of 8 and 9 into double-stranded RNA by PV RdRP. Complexes of RNA template and PV RdRP were incubated for 3 min, 8, 9 or the natural NTP (0.5 mM) was added respectively, and the reaction was allowed to proceed at 30 °C for 1, 5 or 10 min prior to separation of oligonucleotides by PAGE. In panel E, the percent incorporation relative to natural NTPs measured from the gel data in A–D is compared.