Influenza A virus (strain X-31, A/Aichi/68, H3N2) grown in the allantoic cavity of SPF eggs was purchased from Charles River Laboratories (Wilmington, MA). The main stock (HA titer: 32768/0.05 mL, EID50: 10 9.5 /mL, protein content: 2 mg/mL) was stored as 20 µL aliquots at -80 °C until use. IAV is a Biosafety Level 2 agent and was handled following an approved biosafety protocol at Stanford University. The commercially purchased virus suspension was directly diluted in vesicle buffer for use in content transfer experiments. DNAlipids were incorporated into the IAV envelope by incubating virus sample at 4 °C on ice overnight. Viruses were lysed by incubating a suspension (15-20 µL of commercially available stock) with lysis buffer at 37 °C for 1 h. The insoluble debris was removed by centrifugation at 21,130 rcf for 30 min at 4 °C. The supernatant was collected for studying the turn-on behavior of the nucleic acid binding dyes and for TEM imaging of vRNPs (Figure ). In the experiments where Proteinase K digestion was performed, SDS-PAGE was carried out to confirm that the viral proteins were completely digested.