FIG. 4.

An expressed ORF3 peptide-luciferase fusion protein exhibits less luciferase activity than does authentic luciferase expressed from reading frame 2. The luciferase activity detected in cells transfected with mutants expressing luciferase reading frame 2 protein (▴) or reading frame 3 fusion protein (•) is compared to that in mock-transfected cells (−), in cells transfected with the luciferase reading frame 2 mutant encoding an inactive RdRp (▪), and in a luciferase reading frame 3 mutant in which the conserved nucleotide sequence was deleted (♦).