Modeling the Budding Yeast Cell Cycle

pds1∆

Simulation:

Change of parameters: ks1pds"=ks2pds"=0.
Length of G1 phase: 40.2 min.
Mass at division: 2.25

Experiments:

Yamamoto, A., Guacci, V. and Koshland, D. (1996). Pds1p, an inhibitor of anaphase in budding yeast, plays a critical role in the APC and checkpoint pathway(s). J. Cell Biol. 133:99-110.
[Abstract] [Article]
Experimental results: Fig. 3 and Table 1, viable.
Comments: Problem for the model. Although the simulation of pds1∆ looks as if cells are viable, but in the model Esp1 is active throughout the cycle even before spindle alignment. Hence, according to our viability rule, the mutant is inviable.

What seems to prevent premature chromosome segregation in pds1∆ is that Cdc5 kinase is required for efficient cleavage of Scc1 by Esp1 (Alexandru et al., 2001) and for efficient dissociation of securin from chromosome arms (Nasmyth, 2001). Presumably Cdc5 is activated by Clb2 kinase only after a significant delay, long enough for chromosomes to align on the metaphase plate. Hence, PDS1 is not an essential gene.

If this role of Cdc5 were incorporated in the model, the problem with pds1∆ might disappear.