Analysis of cell viability by counting trypan blue-stained cells. HeLa cells were transfected with Lipofectamine with various siRNAs or no siRNA. Three siRNA duplexes, including hSpt5 siRNA (yellow), mismatch hSpt5 siRNA (light blue) and siRNA targeting human capping enzyme (HCE, red), were used in these experiments. Controls for viability included cells mock-transfected with no siRNA (dark blue) or cells transfected with single-stranded antisense hSpt5 siRNA (purple). At various times after transfection, cells floating in the medium were collected and counted in the presence of 0.2% trypan blue. Cells that took up dye (stained blue) were counted as not viable.