Fig. 3.

ATP substantially enhances the error-prone ribonucleotide incorporation by SARS-CoV-2 holo-RdRp. The low-fidelity ribonucleotide incorporation by SARS-CoV-2 RdRp was monitored in the presence of different combinations of ribonucleotides, one NTP (A), two NTPs (B), and three NTPs (C). Two different concentrations of ribonucleotides (200 μM and 2 μM of each NTP) were used with the RNA substrate shown in Fig. 1A. These results suggest that ATP substantially enhances the low-fidelity RNA replication by SARS-CoV-2 RdRp. The 20 nucleotides of the RNA template that is extended by SARS-CoV-2 holo-RdRp include all four types of NTPs (five As, eight Us, five Cs, and two Gs) with the first two sites for incorporation of U.