To determine the localization of GM1 during SV40-induced vacuole formation late during infection, infected and mock-infected CV-1 cells expressing fluorescently-tagged Lamp1-RFP fusion protein were treated with fluorescently labelled GM1 (BODIPY-GM1) and analyzed by confocal microscopy at 48 h.p.i. In contrast to mock-infected cells where GM1 displayed diffuse punctate staining, in infected cells, GM1 (as well as the late endosomal/lysosomal marker Lamp1) was present at the limiting membrane of vacuoles (Figure 1C). This evidence concerns the gene LAMP1 and infection.