β-gal positivity after cotransfection of pCMVβ and wild-type or mutated preprocathepsin G forms to COS-7 cells. COS-7 cells (50 × 10³) were transiently cotransfected with 0.2 to 0.3 μg of pCMVβ and (•) pcDNA3/CatG, (▴) pcDNA3/CatG/Gly₂₀₁/▵Gly₁₉Glu₂₀, or (▪) pcDNA3/CatG/▵Gly₁₉Glu₂₀ in equal or double amounts in six 12-well plates using the DEAE-dextrane method. Cells were stained using the β-gal kit and the absolute numbers of β-gal–positive cells were determined in a light microscope. The diagram shows the mean values of β-gal–positive cells 1 to 4 days after transfection. Values are from 4 separate experiments (with 8 wells counted on day 3).