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. 2022 Apr 27;5:391. doi: 10.1038/s42003-022-03277-0

Fig. 1. Design principles of the inhibitor-off system for quantifying 3CLpro activity and chemical inhibition.

Fig. 1

a–c Schematics of the constructs leading to the current biosafety level 1 system consisting of VSV-∆L-dsRed and Lenti-GFP-3CLpro-L with blasticidin resistance cassette (BlastR). Lentiviral transduction yields GFP-positive cells, and subsequent infection with VSV-∆L-dsRed particles yields GFP/dsRed-positive cells (yellow in merge). Addition of a 3CLpro inhibitor suppresses the accumulation of dsRed signal (inhibitor-off system). d Schematic of FluoroSpot Counter workflow to generate high-throughput data. e GC376 causes a dose-responsive suppression of dsRed signal (inhibitor-off) and a corresponding restoration of cell viability (n = 3 biologically independent replicates per condition with individual data points shown and average values represented by histogram bars).