Fig. 5.

Stage specificity of recombinase expression. The percentage of fluorescent oocysts of the FluSpo clone and of the progeny of a TARGET × DELETER parasite cross was estimated at various days postinfection. GFP expression controlled by the CS regulatory sequences, as in the FluSpo recombinant locus, results in 100% fluorescent oocysts from day 6 onward. When a similar locus is created upon SSR controlled by the TRAP regulatory sequences (note that the residual FRT site in the TARGET/Exc locus is located inside the GFP coding sequence, not in the 5′ CS upstream region), the first fluorescent oocysts are detected in significant numbers only from day 12 onward.