There were two key components of this vector system: (i) the
rtTA2
s
M2 reverse tetracycline transactivator sequence under the
control of the PGK promoter, and (ii) theGFPmarker gene downstream of the miniCMV promoter, which is activated by rtTA2
s
M2
in cooperation with tetracycline. The initial version of this vector
system consisted of two different retrovirus vectors each of which
carried one of the two components mentioned above[16–1. This
study, however, simplified the experimental procedure by combining the two components into a single vector containing all the elements in a single cassette (Fig. 1). Among farm animals, the first
successful application of this single vector system was reported
in a pig model.