INTERFERENCE BETWEEN ANIMAL VIRUSES 189 



C. Perspectives 



It seems presumptuous to speculate on mechanisms of interference at a 

 time when the field is conceptually far ahead of its methodology. It is reassur- 

 ing that new methods are rapidly becoming available with which to test 

 various hypotheses. Critical work on interference, as on other phases of the 

 infectious process, depends on quantitative assay methods, study of single 

 cell yields, genetic analysis of viral progenies, and biochemical characteriza- 

 tion of the viral life cycle. The increasing weight of evidence for the essentiality 

 of viral RNA as the basic multiplying unit of various animal viruses (Colter 

 et at., 1957; Wecker and Schafer, 1957) may direct future efforts toward 

 analogies to mechanisms controlling biosynthesis of constitutive or induced 

 enzymes. As seems to be the case in interference, so here these mechanisms 

 are concerned with permeability problems (Cohen and Monod, 1957) as well as 

 direct competitive inhibition (Cohn, 1957). At another elementary level, 

 further knowledge on interference between animal as well as bacterial viruses 

 will undoubtedly be stimulated by the findings on interference between DNA 

 preparations in bacterial transformations (Hotchkiss, 1954; Alexander et al., 

 1954) which, according to a recent report by Schaeffer (1957), is due to 

 inability of the DNA to penetrate into "interfered" bacterial cells. Ultimately, 

 the evolution of a unified concept of interference will come when the single 

 mammalian cell, uninfected or virus-infected, has become a well-defined, 

 functional, genetic, and biochemical entity. 



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