For RdRp, we were unable to obtain the stable trimeric complex of Nsp7/8/12 (see Supporting Information Section 4.2.1), and therefore we used only the Nsp12 subdomain. As a first control, we tried Remdesivir metabolite GS-443902, but could not detect binding. This is because the latter compound inserts itself into the RNA chain during polymerization, and therefore inhibits RdRp function, but it does not bind efficiently to Nsp12. Instead, Suramin was used as a control with a determined K D = 827 ± 306 nM (over 4 triplicate measurements). Dilution (8-point) series from 0.5 nM to 250 µM were performed on 147 predicted compounds, and after pre-selection of 8 compounds and further triplicate 12-point experiments, 2 high-micromolar binders were identified: Nsp12-1 and Nsp12-2 (see table 3 below). Three additional compounds led to Nsp12 aggregation, so no