The eukaryotic cell cycle is driven by a biochemical oscillator

Few cellular processes are as crucial as that governing cell division. The tight control of cell division indeed plays a prominent role in development and differentiation, while unrestrained proliferation is associated with the cancerous state. The control of the eukaryotic cell division cycle therefore represents a central issue in cell biology (for reviews of recent experimental advances, see the special issues of Science, 246:603-640 (1989) and of the Journal of Cell Science, Suppl. 12 (1989), as well as volume LVI of Cold Spring Harbor Symposium on Quantitative Biology (1991), and Cross et al., 1989; Hunter, 1992; Norbury & Nurse, 1992; Murray & Hunt, 1993; Heichman & Roberts, 1994; King, Jackson & Kirschner, 1994; Nurse, 1994; Peter & Herskowitz, 1994; Sherr, 1994). The cell cycle is classically portrayed as a sequence of phases (fig. 10.1): following mitosis (M) come, successively, the Gx phase leading to the S phase of DNA replication, and the G2 phase, which separates the latter from the next M phase; sometimes cells stay in a quiescent phase, Go, prior to their entry into Gt. The fact that in dividing cells mitosis recurs at regular intervals (whose duration, varying with the cell type, ranges from 10 min up to 24 h or even more) has for a long time raised the possibility that the cell cycle is driven by a continuous biochemical oscillator.