For vaccine use we might aim to maximize the immunogenicity of VSV or a VSV-based vector through the expression increase of VSV G gene or inserted foreign gene while minimizing their potential pathogenicity by growth attenuation. Given such design goals, specifically for a VSV vaccine, we might prefer strain GPM, which showed the highest expression of G protein (Figure 7 ) and the lowest production of virions [18] . Toward such favorable features, Flanagan et al. previously constructed three VSV strains having the following gene orders: 39-G-N-P-M-L-59 (G1N2), 39P-M-G-N-L-59 (G3N4), and 39-G-P-M-N-L-59 (G1N4) [39] . These genome constructions were based on their intuitive idea that translocations of G gene and N gene to earlier and later positions, respectively, compared with wild-type, could not only increase the expression of G protein, but also attenuate virus growth [39] . This idea was supported by their experimental results [39] .