Figure 1.

SARS-CoV genome organization, reverse genetics and nsp14-ExoN motifs and mutations. (A) SARS-CoV genome. ∼29.⁷ kb single-strand (+) RNA. ORF1ab replicase gene is shown in gray with nonstructural protein domains (nsp) 1–16 indicated. Putative RNA synthesis proteins are indicated as in text. Nsp14/ExoN is yellow. (B) Schematic shows nsp14 with three ExoN motifs in red and zinc finger motif hatched. (C) Alignment and MHV and SARS-CoV nsp14 motifs, with conserved active site residues in red. Location of alanine substitutions are indicated, with resulting mutant.