Figure 1. The MultiBac vector system consists of an array of small synthetic DNA plasmids called acceptors and donors (A). Both classes contain a dual expression cassette (polh and p10) with eukaryotic polyadenylation signals (SV40 and HSVtk). Propagation of acceptors is driven by a regular origin of replication (ori^ColE1), whereas donors have a conditional origin (ori^R6Kγ) that requires special bacterial strains for replication. For selection in E.coli, acceptors contain a gentamycin resistance gene (Gn^R) and donors one antibiotic marker (Ab^R). For introduction in the MultiBac viral genome all vectors are equipped with a LoxP site and acceptors additionally with Tn7 transposition sites (Tn7L, Tn7R). Vectors are designed for an easy multiplexing of expression cassettes by the presence of specially designed restriction sites (B). Multigene constructs can futher be generated by fusing several donor vectors with one acceptor vector (C).