S. SPIEGELMAN AND A. M. CAMPBELL 



the one originally present and (b) active templates produce some- 

 thing which activates inactive templates. Both may operate; 

 however, the functioning of the second mechanism is directly 

 implied by the experiments of Rotman and Spiegelman (65) 

 which show that inactive sites preexist and can be converted to 

 active ones. Under the circumstances, the self-duplicating 

 property can be abandoned as being superfluous for a descrip- 

 tion of enzyme-forming system as a protein-synthesizing machine. 

 What the active templates might produce which would activate 

 other ones is also not deducible from the data. However, the 

 only thing the template can be presumed to produce hetero- 

 catalytically is enzyme. One is then led from this model to 

 conjecture that the enzyme molecule itself is the activator of 

 inactive templates. 



The picture of the mechanism emerging is clear, and we 

 may now generalize and formalize it. Let us denote the relevant 

 templates by T, inducer molecules by I, and enzyme by E. 

 We postulate then the following. 



7. When cells have been grown for many generations in 

 the absence of inducer, their templates are all, or nearly all, in 

 the simple and inactive form T. 



2. The complex T-E is unstable and can occur in either 

 one of two ways. In a noninduced cell each T has a small 

 probability of fabricating spontaneously an enzyme molecule. 

 Secondly an induced cell allowed to grow in the absence of in- 

 ducer will, when the inducer is sufficiently diluted, produce T-E 

 from decomposition of the inducer-T-E complex, mentioned in 

 the next statement. 



3. The reaction 



T-E + nl > T-I„-E 



is rapid and relatively irreversible. Here, n is the number of 

 inducer molecules bound per T-E complex; n may be unity in 

 some cases and greater in others. 



4. A population of cells grown in an inducer-containing 

 medium has most, or all, of its sites in the form of T-I„-E. 



144 



