INDUCED ENZYME FORMATION 



was proposed that the transformation of a negative into a posi- 

 tive cell does not involve the de novo formation of active particles 

 but rather the activation of preexistent inactive units. We thus 

 have two categories of particles, active and inactive. A third 

 type was revealed through an analysis by Campbell and Spiegel- 

 man (10) of the growth of active particles. This third kind is 

 intermediate to the active and inactive varieties and is charac- 

 terized by being easily converted by inducer to an active unit — 

 an event which is rare with the inactive particles. We will 

 designate this intermediate type as convertible particles. Their 

 presence is indicated by an abrupt rise in active particle number 

 when reverting positive cells are exposed to inducer. Subsequent 

 increase of active particles obeys an approximately exponential 

 law. The convertible particles occur with increasing fre- 

 quency as positive cells are allowed to go through dilution 

 growth in the absence of inducer. Further, they appear to 

 suffer decay, since if they are not brought into contact with in- 

 ducer soon after their appearance, activation by inducer is no 

 longer possible. 



Another peculiar feature which emerges from a study of the 

 late portion of the reversion is an anomalous change in stability 

 of active particles. It was shown in one of the earlier studies 

 noted (89) that active particles are perfectly stable in the early 

 reversion divisions. However, it was found (81) that this stabil- 

 ity disappeared after about the seventh division in the absence of 

 inducer. 



A Model of Enzyme-Forming System Relating 

 Template, Enzyme, and Inducer 



In discussing the information derived from genetic ex- 

 periments we have deliberately used such neutral words as 

 particles, units, and elements. 



We should now like to essay a synthesis of the biochemical, 

 kinetic, and genetic information we have reviewed thus far in 

 terms of the simplest model consistent with the known observa- 

 tions. 



141 



