Modeling the Budding Yeast Cell Cycle


The components of the model and their function

The regulatory proteins that control the activities of Cdc28 and ensure the proper progression of cell cycle events are listed below.


Cyclin-dependent kinase.
Cln3 G1-cyclins initiating Start events.
Bck2 Protein initiating Start events.
Cln1,2 Cyclins involved in budding (represented as Cln2 in the model).
Clb5,6 B-type cyclins appearing late in G1, involved in DNA synthesis (represented as Clb5 in the model).
Clb1,2 B-type cyclin essential for mitosis, present in S/G2/M phase (represented as Clb2 in the model).
Sic1 Stoichiometric inhibitor of Cdc28/Clb2 and Cdc28/Clb5.
Cdc6 Stoichiometric inhibitor of Cdc28/Clb2. Also a licencing factor for DNA replication.
APC Anaphase Promoting Complex, a multi-enzyme complex reponsible for the degradation of Clb2, Clb5, and Pds1, and it requires Cdc20 or Cdh1 as a cofactor.
IE Intermediary enzyme, a hypothetical protein involved in activating Cdc20 in the model, now identified as the phosphorylated form of the APC core.
Cdc20 Activator of the APC; protein involved in Clb2, Clb5 and Pds1 proteolysis, and required for exit from mitosis.
Cdh1 Activator of the APC; protein involved in Clb2 and Pds1 proteolysis.
Pds1 Stoichiometric inhibitor of Esp1 that prevents sister chromatid separation.
Esp1 Separin protein required for sister chromatid separation.
PPX Hypothetical, Pds1-inhibitable phosphatase that keeps Net1 unphosphorylated, thereby sequestering Cdc14 in the nucleolus, functionally equivalent to the "opposite of FEAR".
Mad2 "Mitosis Arrest Deficient" -- checkpoint protein that keeps Cdc20 inactive until the chromosomes are properly aligned.
Bub2 "Budding Uninhibited by Benomyl" -- checkpoint protein governed by spindle orientation.
Lte1 GTP-exchange factor, present in the bud, and an activator of Tem1.
Tem1 GTP-binding protein and a component of the MEN pathway.
Cdc15 Kinase essential for late nuclear division and a component of the MEN pathway.
Net1 Nucleolar protein and a stoichiometric inhibitor of Cdc14.
Cdc14 Phosphatase required for exit of mitosis.
Swi5 Transcription factor for Sic1 and Cdc6.
SBF Transcription factor for Cln2.
Mcm1 Transcription factor for Clb2, Cdc20 and Swi5.
MBF Transcription factor for Clb5.