Figure 5: Yeast cell sensitivity to CPT depends on the expression of an active DNA topisomerase I from Cryptosporidium spp. (a) MBY3 yeast cells were transformed either with the YCp-GAL, vector empty, or carrying the wild type CpTopIB, in the presence or absence of 50  M CPT (dissolved into 1% DMSO) at . After 3, 6, 24, and 48 hours aliquots were serially diluted and plated in Petri dishes containing yeast culture medium plus 1% dextrose. (b) Dose-response curve showing the inhibitory effect of CPT on yeast cell growing after 24 hours galactose induction. The number of colonies were determined at 30 and plotted relative to the number of colonies obtained at . Data are the average of five different experiments.