STRUCTURAL AND CHEMICAL ARCHITECTURE OF HOST CELLS 19 



cell in growth and in infection. It appeared to have been demonstrated that 

 the viruses then isolated did not contain the metabolic equipment essential 

 for the provision of energy and of intermediary metaboHtes essential to virus 

 spithesis (Stanley et al., 1945; Cohen, 1947, 1955; Gottschalk, 1957a). In a 

 negative way, these findings defined the apparent nature of viral parasitism 

 in terms of the metabohc dependence of the virus upon its host. 



It had been shown that the smaller viruses contained a more limited 

 variety of substances than do any cells. Thus they possessed only a single 

 type of nucleic acid, either ribose nucleic acid (RNA) or deoxyribose nucleic 

 acid (DNA), in contrast to all cells which contained both nucleic acids^ 

 (Cohen, 1947, 1955). The viruses lacked an internal pool of intermediary 

 metaboHtes (Cohen and Anderson, 1946); these had to be provided by the 

 cell in which polymer synthesis leading to virus multiplication occurred. 

 Further, when tests were made for specific enzymes involved in glycolysis, 

 dehydrogenation, respiration, or other of the common degradative paths, 

 these had been negative, although it must be noted that few if any of the 

 enzymes of the biosynthetic paths leading to the amino acids, nucleotides, or 

 combinations of these had ever been sought, nor could they have been before 

 this last decade. 



As reviewed on numerous occasions (Cohen, 1949; Gottschalk, 1957a), the 

 host cell appears to provide most of the low molecular building blocks not 

 supplied in the external medium, as well as the energy for their biosynthesis 

 and coupling into larger viral-specific units. It appears evident that a 

 biochemical understanding of the events occurring in the various phases of a 

 multipHcation cycle requires a systematic comparative study of the inter- 

 mediary metabolism of normal and virus-infected cells. It can be hoped that 

 such a comparative study wiU do much to explain the cytopathological effects 

 of virus infection, and in so doing wiU provide important clues which might 

 lead to the development of a chemotherapy of particular virus diseases. Such 

 expectations have more or less come to fruition in the chemical analysis of 

 a few bacteriophage systems, iti which the biological attributes of the 

 systems have been favorable for chemical study and in which the bio- 

 chemical approaches have at least been contemporary. 



It is true that the biology of animal virus systems are only now becoming 

 similarly amenable to biochemical investigations. Nevertheless, with the 

 exception of the study of the enzyme of influenza virus, to be mentioned 



^ However, as will be seen below, it has occasionally been reported, although as yet 

 unconfirmed, that certain gametes lack one or another of the two main types of nucleic 

 acids. Some organisms, such as the rickettsiae and microbes of the meningopneumonitis- 

 psittacosis group, formerly classified as viruses but more recently excluded from this 

 category, appear to contain two kinds of nucleic acid (Cohen, 1955) and possess other 

 attributes more commonly associated with metabolically active cells. 



