Effect on cell growth rates of RNA interference-based knockdown of mitochondrial proteins in procyclic forms of Trypanosoma brucei. Four typical growth curves are shown: A: reference cell line (transfected with an ‘empty’ RNAi vector and tetracycline-induced); B: no effect; C: moderate effect; D: severe effect. Procyclic forms were grown in the presence of tetracycline to induce RNAi (+Tet, closed squares), and cell growth was monitored daily for 8 days. Growth curves for uninduced cell lines (−Tet, closed lozenges) are shown for comparison. Insets: silencing was confirmed by Northern blot, using the gene GPI8, constitutively expressed in procyclic trypanosomes, as a loading control; at day2, total RNA was purified and Northern blots were performed to assess levels of mRNA. See definition criteria of the effects on cell growth in Methods.