Figure 1.

Expression, purification, and characterization of the SARS-CoV and SARS-CoV-2 RdRp complexes. A, SDS-PAGE migration pattern of the purified enzyme preparations stained with Coomassie Brilliant Blue G-250 dye. Bands migrating at ∼100 kDa and ∼25 kDa contain nsp12 and nsp8, respectively. B, RNA synthesis on a short model primer/template substrate. Template and primer were both phosphorylated (p) at their 5′-ends. A radiolabeled 4-mer primer serves as a marker (m). G indicates incorporation of the radiolabeled nucleotide opposite template position 5. RNA synthesis was monitored with the purified RdRp complexes representing WT (wt, motif C = SDD) and the active-site mutant (motif C = SNN).