Figure 1. Tachyzoite strain 13-20C2 carries a lethal mutation that is conditional with respect to temperature.

(A) The growth of parental RHΔhxgprt and mutant 13-20C2 parasites were monitored in populations partially synchronized by limited invasion over a 32 h period at 34°C and 40°C. The arrow indicates a post-invasion time when cultures were shifted to 40°C. To determine average vacuole sizes, randomly selected vacuoles (>50) in three independent cultures per strain and temperature condition were directly monitored by light microscopy. (B) The lethality of the temperature defect was determined by plaque assay. Freshly invaded mutant parasites were incubated at 40°C for the indicated times before the cultures were shifted to the permissive temperature (34°C) to allow for plaque development. Plaque numbers represent the average of three independent flasks.