FIG. 1.

R₋₃ is not required for CVB3 production, but a transversion at G₊₄ is lethal. The optimal Kozak consensus (RCCAUGG) is shown, along with the equivalent sequences of wt CVB3 and the three mutant viruses, for which the mutated base(s) is shown in gray. The four full-length RNAs were transfected into HeLa cells and, 24 h later, the supernatants were tested for the presence of infectious virus. Despite multiple attempts, no virus was detected in the supernatant of cells transfected with the Koz4 or Koz1,4 RNAs. In contrast, the wt and Koz1 RNAs yielded viruses, which were titrated (plaque morphologies are shown) and named the P1 stocks.