Each clone was induced with 0.5 μg ml-1 tetracycline. After 24 hours, extracts were tested for luciferase activity (Methods). Each extract was assayed in triplicate. Controls were identical cultures maintained in the absence of tetracycline. The activity is represented as mean relative light units per 5 × 104 epimastigotes. Figures in parentheses represent standard error of the mean.