Fig. 4. Effects of double knockdowns of CRK1 and CRK2 on the growth and cell cycle progression in bloodstream-form cells. (A) Cloned bloodstream trypanosome cells harboring the CRK1+CRK2 RNAi plasmid construct were incubated in culture medium at 37°C without (-Tet) or with 1.0 µg/ml tetracycline (+Tet). Cell growth was monitored daily and cell numbers plotted on a logarithmic scale. The inset shows the semi-quantitative RT-PCR assessment of intracellular mRNA levels after a 3-day RNAi induction. -Tubulin mRNA (TUB) was included as a sampling control. (B) Samples of the CRK1+CRK2 knockdown cells over 4 days were stained with propidium iodide and subjected to FACS analysis for DNA content. The histograms from the FACScan are presented on the left and the percentages of cells in G1, S and G2-M phases determined by the ModFitLT software are plotted on the right.