S. SPIEGELMAN AND A. M. CAMPBELL 



Let US first consider an hypothesis (55) which would explain 

 the autocatalytic property in terms of enzyme function analogous 

 to that advanced to explain the kinetic data. Under this 

 hypothesis, the possession of a small amount of galactozymase can 

 efTect the generation of more galactozymase by virtue of the fact 

 that this enzyme system is involved in the energy-generating mech- 

 anism to the cell. The role of the galactozymase in this hy- 

 pothesis is confined to the supply of energy. The active particles 

 would then be "aggregates" of sufficient amounts of galacto- 

 zymase to serve as energy generators. Campbell and Spiegel- 

 man (11) used a respiratory deficient strain to demonstrate that 

 functional enzyme is lost long before the autocatalyst necessary 

 for further enzyme synthesis, and hence these two cannot be 

 identical. 



The quantitative results which were obtained in the study 

 of the reversion from the positive to the negative state led to the 

 formulation of a relatively precise hypothesis concerning the 

 detailed nature of the reversion process. The hypothesis may 

 be summarized in the form of the following series of statements : 

 ( 7) the distribution of active particles among cells is assumed to 

 be normal, (2) during growth in an inducer-free medium these 

 particles neither decrease nor increase in absolute number and 

 hence the average number per cell decreases exponentially, 

 (3) the particles are distributed at each division randomly with 

 equal probability to the mother cell and to the bud, and (4) the 

 minimal number of active particles that a cell must contain in 

 order to score as a positive is close to one. 



These properties were derived solely from a study of the 

 transformation from the positive to the negative state. Anal- 

 ysis of the reverse process quickly led to other features which 

 illuminated further details of the process. Rotman and Spiegel- 

 man (65) were able to convert a large percentage of negatives to 

 the positive phenotype by treatment with fractions of yeast 

 extract. It was possible to show that each of the positive cells 

 so obtained acquired only a few active particles as a result of the 

 conversion. On the basis of the properties of the conversion it 



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