Figure 8.

Model for MBF activity in the mitotic cell cycle. Loss of either Res subunit results in MBF complexes that cannot be regulated in response to cell cycle progression. (1) Cdc10–Res1 complexes (Δres2 cells) have high activation potentials. (2) Cdc10–Res2 complexes (Δres1 cells) have low activation potentials. (3) In wild-type cells the MBF complex contains both Res1 and Res2 throughout the cell cycle. The transactivation potential of this heteromeric complex can be switched from “high” in G1 and S phase to “low” in G2. The C-terminal region of Res2 and a domain overlapping the N-terminal ankyrin repeat are important for this process. (4) The C-terminal region of Cdc10 is also important for regulation because the MBF complex in cdc10-C4 cells is unable to mediate downregulation despite containing both Res1 and Res2.