118 CYTOCHEMISTRY OF PROTEINS 



reconstituted. It is thus not surprising to find the neurons so 

 rich in nucleic acid. If, however, the nerve axon is severed there 

 is a marked decline in cytoplasmic nucleic acid, followed by a 

 recovery as regeneration proceeds. 



Thus the evidence shows that there is a widespread association 

 between protein production and high nucleic acid contents of 

 cells. 



Biochemical Studies of Protein Synthesis 



E. S. G. Barron has studied protein synthesis in bone marrow, 

 using isotopic phosphorus to detect phosphorus turnover in the 

 nucleic acids. In this system cytoplasmic protein synthesis is 

 very rapid indeed. But there is no detectable turnover of nucleic 

 acid phosphorus. 



The reproduction of bacteriophage is another fascinating sys- 

 tem. Type T phage growing in E. coli contain a large amount of 

 deoxynucleic acids: they may thus be regarded as providing a 

 model experiment in nuclear-protein formation of the type con- 

 cerned in chromosome reproduction. The facts have been sum- 

 marized by Seymour Cohen (1949). 



In the growth phase, normal E. coli produce about three times 

 as much pentose nucleic acid as deoxy nucleic acid. When the 

 bacteria are infected with phage T2r+, nucleic acid formation 

 appears to stop abruptly. Protein synthesis, on the other hand, 

 proceeds rapidly at a linear rate. Then, at approximately 7 

 minutes after infection, deoxy nucleic acid formation recom- 

 mences, at a linear rate which is about four times the normal rate 

 of formation. There is no significant formation of pentose nucleic 

 acid. Thus protein formation substantially precedes formation 

 of new deoxy nucleic acid. It was shown by Hershey, Kalmunson, 

 and Bronfenbrenner that T2r+ phage does not react with anti- 

 sera to E. coli; consequently, the protein which is formed is not 

 bacterial protein but a new antigen. The time relationships of 

 formation of new protein and nucleic acid after infection are 

 shown in Fig. 6. 



From the data obtained with phage it is clear that after infec- 

 tion substantial protein synthesis occurs without the formation 

 of new nucleic acid. It could be concluded that the formation of 

 the specific protein of phage does not involve participation of 



