Fig. 1

The cell cycle and check points. The cell cycle is an essential mechanism of cell proliferation, it can be divided into five stages: stationary phase (G0), pre-DNA synthesis (G1), DNA synthesis (S), post-DNA synthesis (G2), and mitosis (M). The whole cell cycle is regulated by a variety of cyclins and cyclin-dependent kinases (Cdks). In addition, G1/S check point, G2/M check point, and spindle check point play an important role in ensuring the normal progression of the cell cycle. R-loop can be formed spontaneously throughout the cell cycle and is most common during the S phase