Modeling the Budding Yeast Cell Cycle

cln1∆ cln2∆ cln3∆ cdh1∆

Simulation:

Change of parameters: ksn2'= ksn2"=0, Dn3=0, kscdh=0, init CDH1=CDH1T=0.
Length of G1 phase: 200 min (requirement for G1 arrest is 201.9 min).
Arrest: Telophase.

Experiments:

Schwab, M., Lutum, A.S. and Seufert, W. (1997). Yeast Hct1 is a regulator of Clb2 cyclin proteolysis. Cell 90:683-693.
[Abstract] [Article]
Experimental results: Fig. 3. "Although cdh1∆ cells are still sensitive to mating factor as they are unable to form colonies, these cells do not arrest uniformly in G1, a fraction of the cell population proceeds through S phase and arrests with 2C DNA content".
Comments: Since mating factor will cause inactivation of all G1 cyclins, we infer from the data of Schwab that the mutant cln1∆ cln2∆ cln3∆ cdh1∆ would have similar behavior as "dh1∆ in the presence of mating factor".

Considering that the simulated cells just barely satisfy our condition for entering S phase, we might expect, in a population of real cells that vary around the mean simulated behavior, some cells will arrest with 1C DNA content and some with 2C DNA content, as observed by Schwab et al.