Recovery of infectious recombinant MHV-GFP. Cell culture supernatants containing viruses produced after virus rescue from two MHV-GFP YAC clones (Clone1, Clone 2) were used to infect 17Cl-1 cells. At 48 hours post-infection, infected cells were visualised for GFP expression (left panels) and by bright field microscopy (right panels). Mock represents 17Cl-1 cells inoculated with supernatant from BHK-MHV-N cells electroporated without viral RNAs. 