34. THE RIBONUCLEIC ACIDS OF VIRUSES 293 



IV. The Ribonucleic Acids of Animal Viruses 



1. Introductory Remarks 



As already discussed in Section II, the animal viruses can be divided into 

 two groups depending on whether they contain DNA or RNA. The range 

 of sizes and the composition of animal viruses is much more variable than 

 that of any known plant viruses. The simplest type of animal virus may be 

 represented by poliomyelitis virus, composed of RNA and protein and 

 morphologically rather similar to turnip yellow mosaic virus. The most 

 complex type is represented by vaccinia virus which contains DNA, protein, 

 lipid, riboflavin, biotin, and copper, and may be more closely related to 

 more highly organized biological units. There are many animal viruses 

 which exhibit all degrees of complexity between these two extremes. Tnere 

 is no correlation between the size of a virus particle and the type of nucleic 

 acid found therein. RNA is present in relatively small viruses such as polio- 

 virus as well as in much larger viruses such as Newcastle disease virus. The 

 same is true for DNA-containing viruses. The relatively small papilloma 

 virus as well as the larger vaccinia virus both contain DNA. 



It has now been shown that RNA is probably the infectious principle 

 for a large number of animal viruses. This has been accomplished by isolat- 

 ing the virus RNA from tissues infected with the virus under consideration 

 or from a purified virus preparation. In all cases, the extraction was done 

 by the phenol method. 58 The method has not been successful with all 

 viruses which have been studied. For example, no infectious RNA has been 

 isolated from Newcastle disease virus or fowl plague virus, both of which 

 belong to the my xo virus group. It is quite possible that this may be due 

 to methodological difficulties in the extraction, but it is also conceivable 

 that RNA may not be the sole agent responsible for infectivity in the case 

 of all viruses. In some cases, other viral components may be necessary in 

 order to initiate infection. 



This discussion of animal virus RNA will be limited to those viruses in 

 which RNA had been demonstrated as the infectious principle and to those 

 cases where at least a chemical analysis has been possible. Of the tumor 

 viruses, the presence of RNA has been well established only in the case of 

 Rous sarcoma virus (about 1 % RNA) 152 ' 153 and the virus of avian myelo- 

 blastosis 153 '" 1 (about 2% RNA); therefore, those viruses are not included. 

 The studies of Latarjet et al. m - 155 and of Hays et a/. 156 who have prepared 



152 R. Bather, Brit. J. Cancer 11, 611 (1957). 



'« M. A. Epstein, Nature 181, 1808 (1958). 



153. j \y Beard, personal communication (1958). 



154 R. Latarjet and M. de Jaco, Compt. rend. acad. sci. 246, 499 (1958). 



