Vector maps of plasmids encoding S1 and S2 RNA segments. Plasmids pP18S1-GPC/MCS (A) and pP18S2-MCS/NP (B) are based on the PICV P18 reverse genetics system plasmid pP18S, which encodes the full-length P18 S RNA segment, followed by hepatitis delta virus ribozyme sequence (HDVribo), under a T7 promoter. Genomic organization of the rP18tri vector expressing eGFP together with influenza virus A/PR8HA (rP18tri-G/H) orNP(rP18tri-G/P). IAV, influenza virus; IGR, intergenic region MCS, multiple cloning sites.