FIG 2.

MERS-CoV ExoN knockout mutants are nonviable. (A) Phenotype of MERS-CoV nsp14 ExoN mutants used in this study, scored at 2 dpt. (B) Comparison of plaque phenotype of selected ExoN mutants in HuH7 cells. Plaque assays were performed using supernatants harvested from transfected cell cultures at 3 dpt, which were diluted 10⁻⁴ for wt and mutant E191D and used in undiluted form for the D90A/E92A ExoN knockout double mutant (DM) and the H229C ZF1 mutant. (C) Immunolabeling (2 dpt) of cell cultures consisting of a mixture of (nonsusceptible) BHK-21 cells transfected with in vitro-made full-length MERS-CoV RNA and susceptible (DPP4-expressing) Vero cells used to amplify any infectious progeny released from the transfected BHK-21 cells. (Left) wt virus; (middle) DM mutant; (right) H229C mutant. Cells were labeled for dsRNA (green) and nsp4 (red). Bar, 100 μm.