Panel A: One step growth curve. TREx-293 cells were infected with wild-type virus (circle) or vtetOI7L in the presence (square) or absence (triangle) of 1 μg/ml TET. Infected cells were harvested at the indicated times and the titer determined on BSC40 cells. Panel B: Rescue of replication. TREx-293 cells were infected with vtetOI7L and transfected with either vector alone (pRB21), plasmid with wild-type I7L driven off of a synthetic early/late promoter (pI7L), plasmid with mutant I7L, mutated in the putative active site, driven off of a synthetic early/late promoter (pI7LH241A), or wild-type I7L driven off of its native promoter (pCB26) in the absence of TET. Infected cells were harvested 24 hpi and the titer determined on BSC40 cells. Transfection of plasmid borne wild-type I7L but not of mutant I7L or vector alone partially rescued the replication of vtetOI7L.