Figure 5

Representative cell cycle and cell density-related changes in Tag. Panel A shows the final cell density versus the initial plating density. Data representing cells in exponential growth are expected to fit an approximate straight line. Data that fall below an extrapolation of that line are at or are approaching density arrest. Panel B shows that the fraction of cells in G₁ increases as a function of density during exponential growth and plateaus as cells arrest. Panels C and D show the G₁ Tag expression as a function of the fraction of G₁ cells (C) or cell density (D). The regions of data used to calculate the rate of change in expression by linear regression are delineated (brackets) and the data used to determine the terminal expression levels are marked (arrows).