Fig. 4

Dose dependence of mutagenesis induced by AFB1. Aflatoxin B1 (AFB1) has been applied at the doses indicated on the X-axis to the classical Ames tester strains and their PolV-deficient derivatives (left panel) or to the new Ames tester strains overexpressing the activated PolRI* and SamA’B polymerase subunits from the uninduced (middle panel) or induced (right panel) lac promoter. The induced His+ revertant counts displayed on the Y-axis were calculated by subtracting the average spontaneous revertant number for a given strain from the total number of revertants per plate values. The strains used are shown in the graph legend and described in Table 1 in detail. To activate the mutagen, 20 min preincubation with rat liver S9 fraction has been carried out before plating as described in the Materials and methods section