Cell-cycle initiation in yeast follows first-order kinetics

THE mitotic cell cycle is an orderly sequence of events, leading to cell division. In mammalian cell lines, a single event in the cycle exhibits first-order kinetics¹, apparently dividing a cell's lifespan into a probabilistic state and a deterministic phase, termed A and B respectively. This rate-limiting event occurs during the G₁ phase^2,3, but its relation to the resting state and to the initiation of the cell cycle is unclear. In this paper we suggest that a probabilistic event exists in the mitotic cell cycle of yeast and that it can be identified with the initiation of a new cycle from the resting state.