Anaphase-promoting complex APC

Two of the four different E3 enzymes mentioned in the text are shown. The cyclosome/anaphase promoting complex (APC) ligates ubiquitin to regulatory and structural cell cycle proteins containing a destruction box as recognition signal (see also 13.3.2). The activity of the APC is thought to be controlled by phosphorylation. Eor simplicity, the subunits of APC are not shown. 

Anaphase. After the spindle has been checked, a sudden loss of cohesion between the sister chromatid pairs allows them to move toward the opposite poles. This process is catalyzed by the anaphase-promoting complex (APC, or cyclosome) and its activator protein Cdc20, a large multiprotein complex.225 The APC also promotes proteolytic breakdown of cyclins and other... 

Fig. 17.2 Top The normal situation the Bub and Mad proteins dissociate from the kinetochore region when the microtubuies are properly aligned. The released Bub/Mad proteins activate a protein (Cdc20) which regulates entry into mitosis and activates the anaphase-promoting complex (APC) and gives the go-ahead fbr entry into the anaphase. Below. The situation when the kinetochore is not attached properly to the microtubules. In this case, the Bub and Mad proteins remain attached to the kinetochore, Cdc20 remains inactive, and APC is not activated. This arrests the cell in metaphase. Thus, the Bub and Mad and Mps-1 proteins in yeast and mammals, respectively, respond to improper assembly of the spindle by arresting cells. (Reproduced with permission of Professor R. A. Weinberg and Nature from Rg. 2 in ref. 8.)...

Two types of E2/E3 complexes are of particular importance for cell cycle control (see Fig. 13.12). One, the SCF complex, is of outstanding importance for the Gj/S transition. The other, the anaphase-promoting complex (APC) or cyclosome, is especially important for the course and control of mitosis. Common to both complexes is the variable collaboration with different proteins to mediate the ubiquitinylation of different substrates. 

Anaphase-Promoting Complex (APC) Controls Degradation of Mitotic Cyclins and Exit from Mitosis... 

The multisubunit anaphase-promoting complex (APC) is a ublqultln llgase that recognizes a conserved destruction box sequence in mitotic cycllns and promotes their polyublqultlnatlon, marking the proteins for rapid degradation by proteasomes. The resulting decrease in MPF activity leads to completion of mitosis. 

We saw earlier that in late anaphase, polyubiquitination of mitotic cyclin by the anaphase-promoting complex (APC) leads to the proteasomal destruction of this cyclin (see Figure... 

The late Gj cyclin-CDK complexes (Clnl-CDK and Cln2-CDK) phosphorylate and inhibit Cdhl, the specificity factor that directs the anaphase-promoting complex (APC) to B-type cyclins, thus permitting accumulation of S-phase B-type cyclins. 

Cyclin A/B-CDKl induce the events of mitosis through early anaphase. Cycllns A and B are polyubiquitinated by the anaphase-promoting complex (APC) during late anaphase and then are degraded by proteasomes. 

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