38. BIOSYNTHESIS OF PROTEINS IN BACTERIAL CELLS 441 



ciated with the microsomal particles of the cytoplasm. Mammalian reticulo- 

 cytes also offer an example of naturally occurring enucleated cells which 

 not only can incorporate amino acids into protein, 174 ' 175 but can also syn- 

 thesize a specific protein, hemoglobin. 176 ' 177 These results seem to indicate 

 that in algae or in reticulocytes, specific protein can be formed in the ab- 

 sence of DNA. 



Interesting information concerning the role of the nucleus in the syn- 

 thesis of specific proteins has also been brought forward recently 63 ' m by 

 studying the metabolic consequences of the radioactive decay in bacteria 

 which have incorporated highly labeled P 32 into the nucleic acids. As will 

 be seen, however, there is a certain discrepancy between the conclusion of 

 such experiments and the data from enucleation experiments reported 

 above. Usually bacteria are grown for a few generations in a medium con- 

 taining highly labeled phosphorus (specific radioactivity 200 to 500 mc. 

 per milligram). They are then frozen at —190° C. and stored to allow the 

 incorporated atoms of phosphorus to decay. At various intervals, the sus- 

 pension is thawed and bacteria are assayed for their ability to produce 

 colonies and to synthesize protein, enzymes, and RNA. Since the use of 

 thymine-requiring mutants permits the labeling either of RNA alone, or 

 of both nucleic acids, it is possible to determine whether the modifications 

 observed in the metabolic pattern have to be correlated with alterations in 

 RNA or DNA. 



The results of these ingenious experiments can be summarized as follows. 

 Bacteria which have incorporated P 32 into their nucleic acids lose the ability 

 to produce colonies according to a precise function of the P 32 decay. The 

 fraction of the surviving bacteria declines according to "multiple hit" 

 kinetics, as if each individual contained a finite number of sensitive units, 

 the preservation of which would permit its survival. Calculation shows 

 that each bacterium contains three such units, that is, as many as nuclei. 

 Accordingly, in uninucleated bacteria, death is a simple exponential func- 

 tion of the fraction of P 32 atoms decayed. Loss of reproductive capacity in 

 bacteria therefore results from disintegration of the DNA. Moreover, when 

 E. coli 15T is labeled in both nucleic acids (by incorporation of P 32 in the 

 presence of thymine), its rate of inactivation is 4 times faster than when 

 RNA is the only nucleic acid labeled. 



Alteration of the DNA by decay of P 32 also results in the loss of enzyme- 

 forming capacity. Thus, after incorporation of P 32 , the capacity to form 



174 I. M. London, D. Shemin, and D. Rittenberg, J. Biol. Chem. 183, 749 (1950). 



175 H. Borsook, C. L. Deasy, A. J. Haagen-Smit, G. Keighley, and P. H. Lowy, J . 

 Biol. Chem. 196, 669 (1952). 



176 A. Nizet and S. Lambert, Bull. soc. chim. biol. 35, 771 (1953). 



177 S. B. Koritz and H. Chantrenne, Biochim. el Biophys. Acta 13, 209 (1954). 



