Rescue of recombinant MERS-CoV and MERS-CoV-GFP. Following delivery of viral RNAs into BHK-21 cells via electroporation the cells were co-cultivated with VeroB4 cells and supernatants containing recombinant viruses produced were used to infect new VeroB4 cells. Infected cells were visualised by bright field microscopy for recombinant MERS-CoV (upper panel; 5 days post infection), and for GFP expression for recombinant MERS-CoV-GFP (lower panel, 3 days post infection). Mock represents VeroB4 cells inoculated with supernatant from BHK-21 cells electroporated without viral RNAs. 