2.5. Subviral Particle Analysis
To probe for subviral particle production, an SVP release assay was used, as described [29]. Briefly, cells were lysed for 20 min on ice, and lysates were centrifuged for 5 min at 15,000× g and 4 °C. To analyze the secretion of SVPs from transfected cells, clarified culture medium was concentrated by ultracentrifugation through a 20% (w/v) sucrose cushion (4 h at 100,000× g and 4 °C), and samples were subjected to Western blot (WB) analysis.