ROLE OF NUCLEIC ACIDS 61 



ated almost completely without effects on enzyme synthesis. These works 

 indicate that in bacteria as well as in higher organisms many proteins can 

 be made in the absence of DNA. 



A completely different approach to the same problem was that of Fuerst 

 and Stent (1956), who studied the consequences of breakages in DNA 

 chains caused by the decay of ^^P previously incorporated in the macro- 

 molecule. E. colt was grown in a medium containing phosphate of fairly 

 high specific radioactivity. The bacteria were then frozen and kept at a very 

 low temperature in order to interrupt all metabolic activities and let the 

 32p decay. After periods of time sufficient for a notable fraction of the ^^p 

 to have disintegrated, the bacteria were plated and tested for viability 

 (ability to form a colony). The experiments showed that the bacteria lose 

 their viability as a result of 32p decay. With thymidine-less mutants in 

 which the synthesis of DNA can be controlled, it could be shown that the 

 loss of viability is largely due to the decay of ^'^P atoms in DNA. 



A very striking fact is that the capacity of making /3-galactosidase is lost 

 at the same pace as viability, although this enzyme is not necessary to cell 

 maintenance or multiplication under the conditions used. Moreover, a few 

 hundred disintegrations of ^sp per bacterium in the DNA are enough to 

 reduce the fraction of viable bacteria, and the enzyme production to 1 per 

 cent. Since E. coli contains several thousand ^ap atoms in DNA, this indi- 

 cates that a relatively small damage to DNA chains can block enzyme 

 production entirely (McFall et ah, 1958). 



These results no doubt indicate a very close dependence of protein 

 synthesis on the integrity of the genetic material and they are in sharp con- 

 trast with the data quoted previously. However, a very puzzling impli- 

 cation of these observations is that the synthesis of a specific protein, 

 j8-galactosidase for instance, is abolished as a result of the decay of ^^p 

 atoms occurring outside the genetic locus of the enzyme. For ^^p decay is 

 certainly random and there are at least a thousand genes; the chances that 

 one 32p decay occurs within the enzyme locus are much too small to explain 

 the observed effects by local action within the locus of j8-galactosidase 

 (Pardee, 1959). Moreover, experiments by Jacob and Wollman (1958) on 

 bacterial conjugation show that ^ap decay can break the linear structure 

 which contains the genes without inactivating the individual loci. 



Since in Stent's experiments destruction in other regions of the genetic 

 material of the bacteria can suppress the synthesis of the enzyme, the effects 

 of 32p decay are not directly relevant to the problem that we are considering 

 at present, namely the personal involvement of the gene in putting together 

 the protein. The effects of ^'^P decay obviously do not concern the control 

 of the structure of an individual protein by a specific DNA region, they are 

 probably more relevant to the control of the concerted operation of bacter- 

 ial biosynthesis by the bacterial genome as a whole. One might be observing 



