292 HEINZ SCHUSTER 



from tomato bushy stunt virus, southern bean mosaic virus, and potato 

 X virus by a method based on treatment of the viruses with detergent, 

 followed by salting out the protein. The virus solutions (~1 %) were heated 

 in detergent (Duponol C) solution (~1 %) for 4 minutes in a boiling water 

 bath. The chilled and dialyzed preparations were heated at 100°C. for 3 

 minutes in 1 M NaCl solution to precipitate the virus protein. The yield in 

 RNA was between 67-87%. The RNA preparations had sedimentation 

 constants between 2-6 S and contained 2-5 % protein. 



Turnip yellow mosaic virus (TYMV)-RNA was first isolated by Mark- 

 ham and Smith 148 • 149 by treatment of the virus with 30 % (v/v) or more 

 ethanol in neutral solutions at room temperature. Cohen and Schachman 150 

 determined the molecular weight of TYMV-RNA which had been pre- 

 pared by alcohol 148 or by heat 53 denaturation of the virus protein. The 

 sedimentation constant lay between S20 = 2 and 4 S. RNA, which had been 

 obtained by heat denaturation of the protein, had a higher sedimentation 

 constant in concentrated solutions than in dilute solutions. This indicates a 

 tendency to aggregate and dissociate reversibly. The RNA solution was 

 polydispersed, which means that only an average molecular weight could be 

 calculated from the sedimentation and viscosity measurements. The weight 

 average molecular weight of the material obtained by heat denaturation was 

 about 10 5 and the corresponding value for RNA liberated by ethanol treat- 

 ment of the virus was about 5 X 10 4 . According to this, a TYMV particle 

 would contain 20-40 RNA molecules. These values are questionable, how- 

 ever, since an RNA prepared from TMV by the method of heat denatura- 

 tion also yields a preparation with an average molecular weight of about 

 2-3 X 10 5 , whereas TMV-RNA prepared by the phenol method has an 

 average molecular weight of about 10 6 . 



Ginoza 90 has shown that treating TMV-RNA at 65°C. for 10 minutes 

 results in a loss of biological activity of 40 % of the RNA molecules, prob- 

 ably by hydrolysis of the polynucleotide chain. Therefore, any method of 

 heat denaturation including longer times of heating appears particularly 

 unsuitable for the preparation of high molecular weight RNA. This is also 

 suggested by the fact that RNA isolated from TYMV under milder condi- 

 tions 151 (10 minutes heating of the virus solution in NaCl phosphate buffer 

 at pH 7.6 and 45°C.) also has a molecular weight less than 10 5 . Most of the 

 RNA released is noninfectious. The slight activity which was found may 

 have been due to nondegraded virus particles. 



148 R. Markham and K. M. Smith, Parasitology 39, 330 (1949). 



149 R. Markham and J. D. Smith, Biochem. J. 49, 401 (1951). 



150 S. S. Cohen and H. K. Schachman, Virology 3, 575 (1957). 



151 J. W. Lyttleton and R. E. F. Matthews, Virology 6, 460 (1958). 



