BIOSYNTHESIS OF PROTEINS 273 



atoms. ^'"^ In this way it has been possible to find a correlation 

 between the rate of synthesis of proteins and the rate of 

 renewal of phosphorus in RNA, the activity of phosphatase, 

 etc. 



Direct evidence of the dependence of protein synthesis 

 on the presence of nucleic acids was obtained by E. F. Gale 

 and J. P. Folkes"" in their work on the incorporation of 

 amino acids into proteins bv fragments of staphylococci 

 which were obtained by disintegrating the organisms by 

 ultrasonic vibrations. Nucleic acids can be removed from 

 these fragments by washing. When this is done they lose 

 their ability to incorporate amino acids and synthesise pro- 

 tein. This ability is, however, restored by the addition of 

 RNA and DNA isolated from staphylococci to the medium 

 in which the fragments are incubated. 



It is very interesting that the ability of disintegrated 

 staphylococcal cells to incorporate separate amino acids into 

 proteins is affected not only by native RNA but also by its 

 breakdown products obtained by splitting it with ribo- 

 nuclease. When this was done there were isolated from among 

 the products several fractions which could bring about the 

 incorporation of amino acids but the incorporation of each 

 different amino acid was accelerated by a particular fraction. 

 Thus, the incorporation of amino acids into the proteins of 

 the cell fi'agments does not require RNA as an intact mole- 

 cular complex but the presence of small fragments of the 

 molecule is enough. Gale therefore considers that the in- 

 corporation of each amino acid may be regarded as a separate 

 and independent reaction associated '^vith a special poly- 

 nucleotide fragment. Recently, however, there has arisen 

 some doubt as to whether this action is due to the individual 

 polynucleotide fragments or to some other active compounds 

 contained in the fraction. 



The study of viruses is of special importance for an under- 

 standing of the part played by nucleic acids in protein syn- 

 thesis, and especially the study of the simplest viruses patho- 

 genic to plants. The most thoroughly studied of these is 

 tobacco mosaic virus, which was discovered by D. Ivanovskii^^^ 

 as early as the end of the nineteenth century. The study 

 of tobacco mosaic virus has made great strides forward since 



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