Figure 5.

Schematic of how Mat3p functions in the Chlamydomonas cell cycle. A single round of the cell cycle is represented by a time line broken into a long G₁ and a short S phase/mitotic period (S/M). The commitment point is also indicated. Mat3p responds to cell size and represses the transition to commitment and, later, the multiple rounds of S phase and mitosis that occur at the end of each cell cycle. When cells are larger than a specific size threshold of ∼178 μm³, Mat3p-mediated repression is lifted, allowing either passage through commitment or continued cell division during S phase/mitosis. Repression is reestablished when daughter cell sizes fall below 178 μm³. Further details are in the Discussion.