34. THE RIBONUCLEIC ACIDS OF VIRUSES 



261 



molecular weight of component A has a value of 1.7 X 10 6 which is in agree- 

 ment with the value obtained by light-scattering. However, the molecular 

 weight of the infectious material, component A, must be larger than 1.7 X 

 10 6 since the value employed for the viscosity in the calculation of molecu- 

 lar weight is actually too small owing to contributions from the inhomo- 

 geneous smaller components (B). In order to determine the molecular weight 

 of component A from the sedimentation constant of this component, it is 

 necessary to investigate the general relationship between sedimentation 

 constant and viscosity of various RNA preparations from TMV-RNA of 

 quite different molecular weights. Figure 3 68 shows this relationship between 

 sedimentation constant and viscosity for different RNA preparations ob- 

 tained by incubating phenol-extracted RNA with ribonuclease for different 

 lengths of time. It may be seen from Fig. 3 that [t?] is approximately in- 



Fig. 3. Relationship between the sedimentation and viscosity constants of TMV- 

 RNA for different molecular weights. Average sedimentation constants s are given 

 in Svedberg units and viscosity constants h] are given in relative units by setting 

 Mo = 1. A 0.2% solution of RNA in 0.02 M phosphate buffer at pH 7.3 was used. 

 From the value [rj]. 4 , it may be deduced that for the RNA component having a sedi- 

 mentation constant s A , the viscosity is a 1.8 multiple of fo]o,. [A. Gierer, Z. Nalur- 

 forsch. 13b, 477 (1958).] 



