246 HEINZ SCHUSTER 



of a cell or virus. One might suspect that ribonucleic acid (RNA) might 

 also serve as genetic material since many types of viruses are known which 

 contain RNA as the sole nucleic acid component. This assumption was ex- 

 perimentally verified by the isolation of biologically active RNA from to- 

 bacco mosaic virus (TMV) by Gierer and Schramm, 3 and by Fraenkel- 

 Conrat. 4 



Virus RNA can be biologically distinguished from cellular RNA through 

 the infectivity of the former. Both cellular and virus RNA are concerned 

 with protein synthesis. The relationship between RNA and protein synthe- 

 sis has already been treated in detail by Brachet (Chapter 28). At that time, 

 however, our knowledge concerning the size and structure of biologically 

 active RNA was still rather slight. Only very recent studies on viral RNA 

 have given us some idea of the properties which an RNA molecule must 

 possess in order to function as a biologically active agent in a living cell. 

 Therefore, in this presentation, the author will emphasize the relationship 

 between constitution and biological activity of RNA. 



II. Viruses Which Contain Ribonucleic Acid; General Remarks 



Viruses can be distinguished from microorganisms chiefly by their smaller 

 size and the absence of metabolic activity outside the host cell. These prop- 

 erties are reflected in the relatively simple structure of viruses as compared 

 with cells. The smallest viruses contain only nucleic acid and protein, but 

 the composition becomes increasingly complex for larger viruses where 

 carbohydrates and lipids may also be present. 



Both types of nucleic acid, DNA and RNA, have been found in viruses 

 although it appears that any one virus type contains only one sort. Early 

 reports on the coexistence of both types of nucleic acid in the same virus 

 have not been confirmed in more recent work employing greatly improved 

 techniques of viral purification. This is especially true for animal viruses. 

 For example, recent analyses of highly purified influenza virus have shown 

 that only RNA is present in this virus, 5, 6 ' 7 whereas earlier studies report 

 the presence of both DNA and RNA. 8 - 9 



3 A. Gierer and G. Schramm, Nature 177, 702 (1956); Z. Nalurforsch. lib, 138 (1956). 



4 H. Fraenkel-Conrat, B. Singer, and R. C. Williams, Biochim. et Biophys. Acta 25, 

 87 (1957). 



B L. Hoyle, 4th Intern. Congr. Biochem., Vienna 1958 Symposium No. VII (1958). 

 6 G. L. Ada, in "The Nature of Viruses" (G. E. W. Wolstenholme and E. C. P. 

 Miller, eds.), p. 104. Churchill, London, 1957. 



7 W. Schafer, in "The Nature of Viruses" (G. E. W. Wolstenholme and E. C. P. 

 Miller, eds.), p. 104. Churchill, London, 1957. 



8 H. K. Miller, Virology 2, 312 (1956). 



9 D. C. Burke, A. Isaacs, and J. Walker, Biochim. et Biophys. Acta 26, 576 (1957). 



