248 



HEINZ SCHUSTER 



TABLE II 



Base Composition of the Ribonucleic Acid of 

 Various Plant Viruses 



" R. Markham and .1. D. Smith, Biochem. J. 46, 513 (1950). 



b J. M. Kaper and R. L. Steere, Virology 7, 127 (1959). 



c D. de Fremery and C. A. Knight, J. Biol. Chem. 214, 559 (1955). 



d R. W. Dorner and C. A. Knight, J. Biol. Chem. 205, 959 (1953). 



e C. A. Knight, J. Biol. Chem. 197, 241 (1952). 



is centrally located and is embedded in a cylindrical protein shell. The 

 internal location of RNA in rod-shaped viruses is in accord with the fact 

 that the virus particle is not inactivated by ribonuclease, whereas isolated 

 infectious RNA is rapidly destroyed. Since the spherical plant viruses are 

 also resistant to ribonuclease, the argument must hold in this case also. 



Although different viruses have different percentages of nucleic acid, the 

 various strains of one type of virus have the same percentage of RNA. 

 This has been shown to be true for TMV 16 ' " and tomato bushy stunt 

 virus, 18 for example. The base ratios of RNA from different strains of the 

 same virus are also approximately the same, whereas the base ratios are 

 quite different for RNA from different viruses (Table II). 



In a comparison of RNA from 5 strains of TMV, Reddi and Knight 19 found a ri- 

 bonuclease-resistant residue after 36 hours of treatment with ribonuclease. After 

 precipitation of this residue with 6% trichloroacetic acid, it was possible to show that 

 the residue had the same base composition in all 5 cases. The residues were rich in 

 purine and deficient in pyrimidine and had an average length of 6 nucleotides. It 



»• C. A. Knight, J. Biol. Chem. 197, 241 (1952). 



17 W. D. Cooper and H. S. Loring, /. Biol. Chem. 211, 505 (1954). 



18 D. de Fremery and C. A. Knight, J. Biol. Chem. 214, 559 (1955). 

 » K. K. Reddi and C. A. Knight, J. Biol. Chem. 221, 629 (1956). 



