Cell size and cell cycle time data were obtained from measurements of S.cerevisiae cells growing in batch culture and from time lapse cinephotomicrography measurements of individual S.cerevisiae cells in steady state £ind perturbed culture conditions. The critical size hypothesis and the transition probability hypothesis of control of proliferation were evaluated simultaneously with these data. It was concluded that a combination of the two hypotheses is more compatible with the data. Two models which combine the hypotheses and which provide good fits to the. data are the Sloppy Size Control model and the Tandem model, although it is necessary to add to the latter that critical size has mean and variance rather than a fixed value. The difference between the parent and daughter circle times is explained by both models as being a consequence of unequal division and the operation of a size control mechanism. However, experiments with perturbed cell cultures indicated that some of the difference in cycle times is due to a factor independent of size. Clonal growth rates were measured and shown to vary significantly within a population, suggesting heterogeneity in individual growth rates. It was concluded from the data from both steady state and perturbed cell populations that although variation in growth rates produces variation in cycle times, a probabilistic mechanism (which also produces variation in cycle times) cannot be excluded, as has been suggested.
|Date of Award||1982|