34. THE RIBONUCLEIC ACIDS OF VIRUSES 



247 



TABLE I 

 RNA-Containing Plant Viruses 



Virus 



Particle 

 weight 



(X io- 6 ) 



RNA con- 

 tent (% of 

 the particle 

 weight) 



RNA 



"molecular 

 weight"" 



Spherical 

 Turnip yellow mosaic 

 Tomato bushy stunt 

 Southern bean mosaic 

 Tobacco necrosis 

 Tobacco ringspot 



Rod -shaped 

 Tobacco mosaic virus 

 Potato X 



5 



10.65 

 6.6 

 8.0 

 3.4 



40 

 36-39 



34 



16.5 



21 



18 



44 



1.7 X 10 6 



1.65 X 10 6 



1.4 X 10 6 

 1.45 X 10 6 



1.5 X 10« 



2.2 

 2.0 



X 10 6 

 X 10 6 



a The RNA content of one virus particle expressed as "molecular weight." 



1. Plant Viruses 



All plant viruses which have been subjected to a detailed chemical analy- 

 sis have proved to contain only RNA. The form and chemical composition 

 of these viruses is relatively simple since they can be classified as either 

 spherical or rod-shaped. All are composed of only RNA and protein, and 

 may be considered to be nucleoproteins. Many of these viruses have been 

 crystallized so that it is possible to subject such viruses to structure analysis 

 by X-ray crystallography. 



In Table I, the sizes and RNA content of some familiar plant viruses are 

 presented. It will be noted that the individual viruses have a highly variable 

 percentage of RNA. However, if the RNA content is compared with the 

 particle weight of the individual viruses, it may be shown that the total 

 RNA per particle corresponds to an RNA of "molecular weight" 1.5-2 X 

 10 6 . 10 It will be shown that this quantity represents the biologically active 

 unit of RNA for the case of tobacco mosaic virus (TMV). 11 



The structure of the virus nucleoprotein has been deduced chiefly on the 

 basis of X-ray analysis. 12 " 15 The RNA of the spherical viruses is centrally 

 located within a spherical shell of protein. In rod-shaped viruses, the RNA 



10 W. Frisch-Niggemeyer, Nature 178, 307 (1956). 



11 A. Gierer, Nature 179, 1297 (1957); Z. Naturforsch. 13b, 485 (1958). 



12 R. E. Franklin, A. Klug, J. T. Finch, and K. C. Holmes, 4th Intern. Congr, Bio- 

 chem., Vienna 1958 Symposium No. VII (1958). 



13 A. Klug, J. T. Finch, and R. E. Franklin, Biochim. et Biophys. Acta 25, 242 (1957). 



14 F. H. C. Crick and J. D. Watson, Nature 177, 473 (1956). 

 16 D. L. D. Caspar, Nature 177, 475 (1956). 



