Figure 1.

Quiescence (G₀)

Quiescence is a reversible G₀ state, because cells retain the ability to re-enter G₁ of the cell cycle after passing the restriction point (R-point) of the G₁/S transition. Cells in G₁ can also enter senescence, which is an irreversible state. E2F mediates transcription of cell-cycle genes. In quiescent cells, E2F is repressed by retinoblastoma (RB) binding. The repressive ability of RB is regulated by the CDK/cyclin complex, which in turn is controlled by CDK/cyclin inhibitors. Adapted from Biggar and Storey (2009).