Figure 1. ß-galactosidase (ß-gal) activity in AxCAiLacZ-infected HSC4 and SAS cells. Cells were infected with AxCAiLacZ at multiplicity of infection (MOI) ranging from 0–25 plaque forming units per cell (pfu/cell). After 24 h, cells were lyzed and ß-galactosidase activity was determined. One unit of ß-galactosidase is defined as the amount of enzyme that will hydrolyze 1 µmol of ortho-nitrophenyl-ß-D-galactopyranoside in 1 min at 37°C.