FACS analysis of PFV particle binding to HeLa cells. (A, B) Histogram data of measured GFP signal intensities obtained after incubation of (A) GFP-tagged wt (PG-GFP) or (B) PGM3 derived (PGM3-GFP) PFV particles, containing (+Env) or lacking (ΔEnv) PFV Env, with HeLa cells. (C) Target cell attachment of Gag-GFP labelled PFV virions was dose-dependent. (D) GFP-tagged particle binding could be competed for by preincubation with untagged PFV particles. HeLa cells were preincubated with untagged PFV particles at different concentrations. After preincubation with untagged PFV particles, the virus-containing solution was replaced by GFP-tagged viruses at equal amounts in each sample.