Cell Cycle Control

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

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