FIG. 4.

The Tet-ON and the Prog systems work with similar efficiencies in several cell types. HeLa cells, Cos-7 cells, NIH 3T3 cells, and 1523 cells were coinfected with 10 PFU per cell of activator and reporter viruses belonging to the respective systems. Inducer (4 μM) was added at the start of infection, and CAT activity was measured at 16 h postinfection. For comparison, CAT expression induced by infection with 20 PFU of AdCMVCAT is shown.