The anaphase-promoting complex: New subunits and regulators

Ubiquitin-mediated proteolysis of cell cycle regulators is a crucial proces s during the cell cycle. The anaphase-promoting complex (APC) is a large, m ultiprotein complex whose ES-ubiquitin ligase activity is required for the ubiquitination of mitotic cyclins and other regulatory proteins that are ta rgeted for destruction during cell division. The recent identification of n ew APC subunits and regulatory proteins has begun to reveal some of the int ricate mechanisms that govern APC regulation. One mechanism is the use of s pecificity factors to impose temporal control over substrate degradation. A second mechanism is the APC-mediated proteolysis of specific APC regulator s. Finally, components of both the APC and the SCF E3 ubiquitin-ligase comp lex contain several conserved sequence motifs, including WD-40 repeats and cullin homology domains, which suggest that both complexes may use a simila r mechanism for substrate ubiquitination.