Cyclic proteolysis
Enzyme complexes act at different times to cause proteolysis of the
proteins of the control system, therefore inactivating them
- Cyclin-Cdk complexes inactivated by cyclin proteolysis
- Occurs by a ubiquitin-dependent mechanism
- Multiple copies of ubiquitin attach to specific amino acid
sequences on the cyclins
- This marks the cyclins for destruction
The key regulator of the metaphase-anaphase transition is the APC/C (anaphase promoting complex or cyclosome), a member of the ubiquitin ligase family of enzymes.
- APC/C catalyses ubiquitylation and destruction of 2 major proteins:
- Securin - protects protein linkages holding sister chromatids together
- S and M cyclins - inactivates most Cdks in the cell