NUCLEOPROTEINS, NUCLEIC ACIDS, RELATED SUBSTANCES 153 



Table 6-1 



Types of protein and nucleic acid found in some typical nucleoproteins 



Composition of nucleoproteix * 

 Source of nucleoprotein Protein, % Nucleic acid, % 



Calf thymus Histone, 40 DNA, 60 



Sperm heads of fish Protamine, 40 DNA, 60 



Liver Lipoprotein, 95 DNA, 5 



Chromosomes of calf thymus: 



Soluble fraction, 90% Histone, 47 DNA, 45 



fRNA 11 

 Residual fraction, 10% Nonhistone, ? ■ „,, . ' „ 



IDNA, 2 



Tobacco mosaic virus Not classified, 94 RNA, 6 



Tobacco ring-spot virus .... Not classified, 60 RNA, 40 



Tuberculin from tubercle 



bacillus Not classified, 60 DNA, 40 



Yeast Not classified, 90-105 RNA, 5-10 



DNA, ? 



Bacteria Not classified, 80-85 RNA, 15-20 



* DNA denotes desoxyribonucleic acid ; RNA means ribonucleic acid. The nature 

 of the different types of nucleic acid will be discussed later. Where no figures regard- 

 ing the amounts are available, this is indicated by a (juestion mark (?) in the second 

 and third columns. 



The viruses of the tobacco plant are well-characterized. They have 

 been obtained in crystalline form and their properties carefully deter- 

 mined. The protein part varies from 60 to 94 per cent of the nucleo- 

 protein in the two viruses listed in Table 6-1. The amino acids of tobacco 

 mosaic virus account for 106 per cent of the virus. (See Table 5-4). 

 The nucleic acid is of the ribose type, which is the most abundant type 

 found in plant material. 



The molecular weights reported for nucleoproteins are large, 2 million 

 for calf thymus nucleohistone and 40 million for tobacco mosaic virus. 



NUCLEIC ACIDS 



Component units 



The nucleic acids are themselves complex structures with molecular 

 weights ranging from 17,000 for yeast nucleic acid to more than a million 

 for the acid from the thymus gland. The particle size varies with the 

 method of preparation, hence, the smaller weights may represent split 

 products of the larger units. The molecules appear to be rod-like in 

 shape, with the length of the particles 40 to 400 times that of their 

 diameter. 



Nucleic acids are divided into two classes depending upon the kind of 

 hydrolysis products. This will be evident from an inspection of the 

 following tabulation. 



