FIG. 2.

Identification of cell culture-adaptive mutations. Huh-7 cells were transfected with the parental replicon 5.1 or replicon RNAs carrying the mutations given above each plate. Numbers below the plates refer to the CFU per microgram of in vitro-transcribed replicon RNA. For comparison, representative plates that were obtained after transfection of each 10 ng of in vitro-transcribed replicon RNA or 1 ng in the cases of the replicons shown in the bottom line are shown. Note that for the determination of the CFU, serial titrations down to 0.25 ng of each RNA were transfected. With the nonadapted replicons, five independent transfections were performed, but with the adapted RNAs, 20 to 50 independent transfections were performed.