QUANTITATIVE CONFIRMATIONS 17 



is no linear relationship between the quantity of RNA per milligram 

 of protein nitrogen and the rate of protein synthesis (Jeener, 1952). 

 If, on the other hand, continuous cultures are used under condi- 

 tions where growth maintains itself during long periods at a con- 

 stant rate which can be varied at will between wide limits, a strict 

 relationship is found between the rate of protein synthesis and the 

 quantity of RNA in excess of a constant basal figure always present 

 in the cells. Thus the close relationship between the quantity of RNA 

 present and protein synthesis exists only for systems in the steady 

 state. When the physiological conditions of the cells are changing 

 rapidly, for instance at the end of the lag and logarithmic phases of 

 growth, no such simple correlation can be found (Jeener, 1953). 



There is further work on microorganisms which strongly suggests 

 that protein synthesis and RNA synthesis are closely linked. DNA 

 synthesis, on the other hand, can be dissociated by various means 

 from RNA and protein synthesis. 



For instance, Jeener and Jeener (1952) have been able, in the case 

 of Thermobacterium acidophilus, to interfere selectively with either 

 RNA or DNA synthesis by removal from the culture medium of 

 uracil and DNA respectively. In the absence of DNA, the cells still 

 grow as elongated filamentous forms, but the number of bacterial 

 nuclei remains small. In cultures deprived of uracil, growth is in- 

 hibited and both nuclei and cytoplasm are affected. These findings 

 indicate that while protein synthesis is dependent on RNA syn- 

 thesis it is much less directly related to DNA synthesis. 



This analysis has been carried one step further by Cohen and 

 Barner (1954, 1955), who worked with quantitative methods on a 

 thymine-requiring mutant of Escherichia coli. They found that in 

 the absence of thymine this organism becomes incapable of forming 

 colonies. This sort of sterilization is accompanied by a marked 

 increase in bacterial length and girth; the RNA content doubles, 

 while there is almost no DNA synthesis. Nevertheless, the organism 

 is still capable of induced enzyme synthesis (synthesis of xylose 

 isomerase, when xylose is added to the medium as an inducer). 

 Synthesis of RNA, protein, and induced enzyme all run parallel in 

 this system in which DNA synthesis has been suppressed. Cohen 



References p. 50/54 



