462 E. A. EVANS, JR. 



The analyses for T2 and T3, reported by Eraser (1957), were performed on 

 purified samples of whole phage (5 to 8 determinations), hydrolyzed in sealed 

 tubes in vacuo with constant boiling HCl at 113.5°C., and analyzed by the 

 ion exchange chromatography procedure of Moore and Stein (1948, 1951), 

 and of Hirs and associates (1954). The values for serine, threonine, and 

 tyrosine have been corrected for loss during hydrolysis. Determinations of 

 tryptophan and of cysteine were not made. The bracketed values for trypto- 

 phan are from analyses of T2 ghost protein by Herriott and Barlow (1957), 

 employing a variety of procedures; the bracketed value for cysteine was 

 reported by Luria (1953) on a phage sample of unspecified purity, using a 

 microbiological teclmique. 



The values for T4 (Poison and Wyckoff, 1948) were obtained several years 

 ago by paper chromatography after HCl hydrolysis and may be less accurate 

 than the values for T2 and T3. The values for the amino acid content of the 

 proteins of E. coli were obtained by chromatographic and radioautographic 

 analysis, after HCl hydrolysis, of isotopically labeled amino acids from cells 

 grown with C^* glucose as the sole carbon source, with the exception of the 

 values for cysteine and methionine (in which S^^ was the isotope used), and 

 the value for isoleucine (based on the incorporation of C^^Og) (Roberts et al., 

 1955). 



Eraser and Jerrell (1953) studied the amino acid composition of the protein 

 portion of T3 mider a variety of conditions and fomid that alterations in the 

 nature and amomit of the carbon and nitrogen sources of the host bacteria 

 were without effect on the quantitative amino acid composition of the viral 

 protein. It is generally assumed that the chemical composition of the other 

 coliphages is also independent of the nutritional state of the host cell. 



While the various coliphage strains show significant differences in amino 

 acid composition as compared with each other and with the host cell, the 

 general pattern of amino acid distribution in bacterial cell and virus is quite 

 similar. In view of the fact that bacterial protein is not appreciably used for 

 the synthesis of viral protein (Siddiqi et al., 1952), the latter bemg manufac- 

 tured de novo from the nutrient materials of the external medium, one might 

 expect differences in protein composition of a considerable degree. However, 

 the values of Table I represent averages for the great variety of protein 

 molecules (enzymes, cell wall components, etc.) present in E. coli and, since 

 there is increasing evidence for the physiological heterogeneity of viral 

 protein (see Section B), it is possible that analysis of the individual proteins 

 of host ceU and virus (when this can be done) wiU exhibit specialized features 

 in structure as well as function. The general similarities in amino acid com- 

 position between total bacterial and viral proteins may reflect the fact that 

 it is the enzymic machinery of the host ceU that must synthesize viral 

 protein. 



