FIG. 3.

Evolution of the −35/+9 promoter region during passaging in cultured cells. In vitro-transcribed RNA from each library was transfected into C7-10 cells (A) or BHK-21 cells (B). The virus produced by the transfected cells were then passaged three or four times at a MOI ≤ 0.1 (see Materials and Methods). Intracellular viral RNA during each passage was isolated, and the STR promoter region was RT-PCR amplified. The RT-PCR product was purified and sequenced directly to obtain the consensus sequence of each population after each passage (P0 = transfected cells). The sequences shown are those of the minus strand.