Schematic representation of the Lassa virus (LASV) replicon particle (VRP) system and single-cycle phenotype. A, Transcripts produced from the VRP rescue plasmids pLasL and pLasSΔGPC+ZsG, as well as the helper construct pCAGGS-Lassa-GPC. B, Lack of VRP spread in Vero E6 cells. Cells were inoculated with LASV or VRPs at a multiplicity of infection of 0.01 or were mock inoculated. Cells were then fixed on days 1, 2, 3, and 7 after infection. Day 7 supernatants were passed onto fresh Vero E6 cell monolayers, and cells were fixed 1 day later. Green, ZsGreen (ZsG) fluorescence; red, immunostaining against LASV NP.