Figure 4.

FACS-mediated cell-cycle analysis of CHO-233₁₇₆ and CHO-226₉₆. Both cell lines were grown for 48 h under conditions allowing for all three expression configurations +Tet/–PI (growth-promoting gene induced, sT for CHO-233₁₇₆ and p27^Kip1AS for CHO-226₉₆), +Tet/+PI (both transgenes repressed) and –Tet/+PI [growth-arresting gene (p27^Kip1) induced] and incubated with the DNA-staining chemical propidium iodide for DNA content-based assessment of cell-cycle distribution. The cell-cycle profiles of proliferation-enhanced (+Tet/–PI) conditions and set-ups which repress the dual regulation unit (+Tet/+PI) are compared to the cell-cycle distribution of the parental cell line CHO-TWIN1₁₀₈ (G₁, 29.5%; G₂, 10.3%; S, 60.2%). In contrast to CHO-226₉₆ cells which arrest in the G₁-phase under –Tet/+PI conditions, CHO-233₁₇₆ cells do not display any accumulation of this cell-cycle phase (see also Figs 3 and 5).