STRUCTURAL AND CHEMICAL ARCHITECTURE OF HOST CELLS 21 



vims multiplication, but also possible sites for chemotherapeutic attack. 

 Although this particular base has not been found in other viruses, it is far 

 too early to say that structurally and metabolically unique units will not be 

 found in other viruses. For example, the specific hydrolase of influenza virus 

 has not yet been found in the host cells in which the virus multiplies (Gott- 

 schalk, 1957a), and the structural basis of this enzymatic activity requires 

 exploration. The C-terminal tripeptide of tobacco mosaic virus and its strains 

 may also be specific unto these viruses and therefore possess unusual meta- 

 bolic interest. 



(4) In addition to the utihty of HMC in following viral DNA through its 

 life cycle, the formation of this compound relates precisely to the problems 

 of possible aberrancy of important biosynthetic paths under the influence of 

 virus infection. For example, that the diversion of cell metabolites to virus 

 synthesis does occur is documented in only a few instances, and the data are 

 most complete in the case of infection of E. coli by the T-even phages. In 

 this extraordinarily virulent infection, the infected cell stops the synthesis 

 of most of its normal polymers, enzymes, etc. (Cohen and Anderson, 1946; 

 Monod and WoUman, 1947; Cohen, 1948), essential building blocks being 

 entirely diverted to viral synthesis. For this case, the hypothesis has been 

 developed that this qualitative alteration in metabolic emphasis is due to 

 the diversion of cytidyhc acid and deoxycytidyHc acid, essential for the 

 synthesis of normal nucleic acid and complementary protein, to form 

 5-hydroxymethyl deoxycytidyHc acid, which is uniquely a component of the 

 DNA of the T-even phages (Wyatt and Cohen, 1953; Cohen, 1953). This 

 process is represented in Fig. 1. 



One should also like to know if the synthesis of HMC nucleotides affects in 

 any serious way the synthesis of phospholipids, discovered by Kennedy (1957) 

 to be mediated via coenzymes containing cytosine nucleotides. Does the 

 formation of HMC also affect thiamine synthesis and utilization, since this 

 vitamin contains an analogous hydroxymethyl cytosine? Does this relate in 

 any way to the accumulation of pyruvate (Spizizen, 1957) observed with 

 E. coli infected by the T-even phages, since thiamine-containing coenzymes 

 are most important in the further metabolism of pyruvate and the other 

 a-keto acids? Will the effect then extend to a-ketoglutarate and thereby 

 control the tricarboxylic acid cycle, glutamate production, etc.? 



(5) There is so Httle known that it is difiicult to predict what one might 

 find. WiU an insect virus contain ortho tyrosine as do some insect cuticles 

 (DenneU, 1956)? WiU a virus infecting apple trees contain 1 -amino cyclo- 

 propane- l-carboxyhc acid (Burroughs, 1957)? Do the E. coli phages contain 

 diaminopimehc acid, which is present in the cell waU of the bacterium, and 

 if not, what is there about the origin and metabolism of these substances 

 which excludes them from virus protein? Can not a new pathway be developed 



