CHEMICAL COMPOSITION 89 



The carbohydrate of T2 is part of the nucleic acid, but that of 

 T7 may be in part a constituent of the phage particle or an im- 

 purity. It is desirable to have additional analyses of this type, 

 since only two serologically distinct groups of phages have been 

 analyzed and this is an inadequate sample from which to draw 

 general conclusions about the chemical nature of phages. 



The gross chemical composition of the few phages analyzed is 

 quite different from the composition of any plant or animal 

 virus which has been analyzed (Beard, 1948). The known bac- 

 teriophages are characterized by a large content of deoxyribo- 

 nucleic acid (DNA). The well known plant viruses contain 

 ribonucleic acid (RNA) exclusively, usually in relatively small 

 amounts. Two, and perhaps three, animal viruses contain pre- 

 dominantly RNA. The latter include the carefully studied 

 PR8(A) and Lee(B) strains of influenza virus (Ada, 1957) which 

 are reported as having 0.9 per cent RNA and 0.1 per cent DNA, 

 and MEF-1 poliomyelitis virus (Schwerdt and Schaffer, 1955) 

 which analyzed 24 per cent RNA and 1 per cent DNA. Nearly 

 10 per cent RNA was found in Eastern equine encephalitis virus 

 by Taylor, Sharp, Beard, and Beard (1943). Wyatt (1952) 

 reported DNA in some insect viruses. 



5. Amino Acids, Nucleotides, and Bases 



Poison and Wyckoff (1948) published the first amino acid 

 analyses for phage T4. The phage was purified by centrifuga- 

 tion, hydrolyzed, and the amino acids separated by paper chro- 

 matography. No criteria of purity were presented and the 

 authors seem to have reservations about the significance of the 

 results. Luria (1953a) reported amino acid analyses of T2 and 

 T4 bacteriophages from his laboratory. Fraser and Jerrell 

 (1953) described in more detail the amino acids in preparations 

 of T3. Hershey (1955) analyzed several protein fractions from 

 T2. The results are summarized in Table IX. The phage pro- 

 teins do not diflfer markedly in composition from plant and ani- 

 mal virus proteins but are quite diflferent from the histones and 



