The yeast cell cycle engine

The yeast cell cycle is regulated by a number of different cyclin-Cdc28 complexes, some of which orchestrate G1 events, and some of which orchestrate G2/M events. G1 cyclins lead to expression of G2 cyclins; the G2 cyclins then repress the G1 cyclins. G2 cyclin expression eventually leads to mitosis, which causes loss of the G2 cyclins, allowing derepression and reappearance of the G1 cyclins. These interactions between different classes of cyclins push the yeast cell cycle forward. Nutrients act through the G1 cyclins to stimulate division, while mating pheromones act through G1 cyclins to inhibit division.