Schematic of the FRET-based assay used by Codding and Trudeau (2018) . (A) FRET signal is detected between hERG channels with the deletion of the PAS domain (hERGΔPAS) tagged with Citrine at the C terminus and isolated PAS domains tagged with CFP. (B) No FRET signal is detected between hERGΔPAS channels with the GG mutations in the intrinsic ligand and isolated PAS domains. The PAS domain is green, CNBD blue, the C-linker light blue, CFP cyan, Citrine yellow, and transmembrane portions of the channel are colored in gray. The intact intrinsic ligand is orange and GG mutant is white.