RELATIONSHIP BETWEEN CELL COMPOSITION AND TIMING OF CELL-CYCLE EVENTS IN FISSION YEAST

The mechanisms for the regulation of cell growth and division are poorly understood. It is possible that mathematical models describing the biochemical processes known to have a role in cell proliferation may be useful in giving an integrated description of the kinetics of cell growth and in suggesting possible regulatory mechanisms. A dynamic model which accounts for the processes of synthesis and degradation of ribosomes and protein, and which also proposes cell size controls over DNA replication and nuclear division, has been proposed by us for eukaryotic cells. Two kinds of models are popular for the control of cell proliferation: cell size models and stochastic models. The former ones propose, as our model does, that cell cycle events such as DNA replication can take place only after the cell size has reached a specific threshold value, whilst the latter models propose that DNA replication occurs at random with a defined probability. It is obvious that cell size models are able to predict defined relationships between cell composition (expressed as protein and DNA contents) and the timing of cell cycle events. Equations for the calculation of the average DNA and protein contents in cells during exponential growth and the latter at nuclear division are derived in this paper. The experimental findings available for fission yeast are shown to agree well with the predicted ones. These results are in favour of the validity of the proposed model, at least for fission yeast. © 1979, International Society of Differentiation. All rights reserved.