Fig. 3.

Quantitation of SKI-1/S1P cleavage and the formation of the mature G1 and G2 subunits. Phosphorimages of the deglycosylated polypeptides represented in Fig. 1B were analyzed using Image Gauge software (Fuji) and the Profile and Background tools to quantitate the radioactivity (PSL units). The efficiency of SKI-1/S1P cleavage was defined as the ratio of PSL units in the sum of the G1 + G2 peaks relative to the total number in both GP-C and G1 + G2 peaks. Results were analyzed for two complete experiments, and the relative conclusions are consistent with those of additional partial studies. Because the absolute efficiency of cleavage varied between experiments, each experiment was normalized to the average extent of cleavage in the entire 19-member panel. This average ratio (16% and 24% in the two complete experiments shown here) was used to determine the relative degree of cleavage in each mutant, and these numbers were averaged to generate the values plotted. By this analysis, the wild-type envelope glycoprotein was cleaved 1.17-fold better than the arbitrary average of the panel; 100% and 50% of the wild-type level are shown as dashed lines. Error bars represent ± one standard deviation.