ISOLATION AND COMPOSITION OF PENTOSE NUCLEIC ACIDS 383 



TABLE I 

 Properties of Crystalline Plant Virus Nucleoproteins 



denature protein might well have a similar destructive effect on the integ- 

 rity of PXA. The possibility cannot be ignored that native PNA, if we 

 could obtain it, would be found to possess alone the biological activities 

 associated with the nucleoprotein. 



The composition of the individual plant virus nucleoprotein is constant. 

 The material isolated from plants infected with turnip yellow mosaic 

 virus consists of only two components: the free protein, and the nucleo- 

 protein containing 28% PNA. Complexes of intermediate PNA content 

 are not found. The compositions of several crystalline plant viruses are 

 presented in Table I. The PNA content of these preparations is constant, 

 regardless of the host, the time of harvest, or the method of isolation. It is 

 further of interest that the different strains of tobacco mosaic virus all have 

 identical PNA content, and even, as will be discussed later, identical 

 nucleotide composition; however, the amino acid composition of their 

 proteins differs.^"' ^* The particle weight of different plant viruses and their 

 PNA content show great variation. Thus, tobacco mosaic virus has a 

 particle weight of 40 X 10^ with a PNA content of 6%, while tobacco ring 

 spot virus with a particle weight of only 3.4 X 10^ contains 40% PNA. 

 If their PNA content is expressed as the number of nucleotides per virus 

 particle, considerably less variation- — only from 8000 to 4000- — is observed. 

 When the assumption is made that each virus particle contains 1 molecule 

 of PNA, the molecular weight of tobacco mosaic PNA would be of the 

 order of 2,500,000; actually, the molecular weight of tobacco mosaic PNA 

 isolated by the mildest procedure^^ was estimated as 300,000. It appears 



3" W. M. Stanley and H. S. Loring, Relazioni del IV Congresso Inlernazionale di 

 -patologia comparata 1, 45 (1939). 



31 C. A. Knight, J. Biol. Chem. 45, 11 (1942). 



32 W. M. Stanley, J. Biol. Chem. 135, 437 (1940). 



33 H. Neurath and G. R. Cooper, J. Biol. Chem. 135, 455 (1940). 

 3" G. L. Miller and W. C. Price, Arch. Biochem. 10, 467 (1946). 

 36 W. M. Stanley, /. Biol. Chem. 129, 405 (1939). 



36 C.A. Knight and W. M. Stanley, J. Biol. Chem. 141, 39 (1941). 



