152 NUCLEOPROTEINS, NUCLEIC ACIDS, RELATED SUBSTANCES 



an electric current through the solution. The positively charged protein 

 moves to the cathode and the negatively charged nucleic acid goes to the 

 anode. Thymus nucleoprotein is an example of this type. The protein 

 is histone, and, since this is a strongly basic substance, it forms a salt 

 with nucleic acid. The two components are probably joined together 

 through the basic groups of arginine, histidine and lysine, and the phos- 

 phoric acid groups of the nucleic acid. Histones and protamines are 

 particularly high in arginine. If a sample of histone or protamine dis- 

 solved in 0.14il/ sodium chloride is added to a solution of nucleic acid 

 having the same strength of sodium chloride, the two components react 

 and form a precipitate. Such precipitates are probably the result of 

 interaction of the molecules as a whole, and not arginine alone. The same 

 quantity of arginine, histidine, and lysine as is contained in the protamine 

 forms no precipitate at the same pH. 



There may be a second type of nucleoprotein in which the protein and 

 nucleic acid are bound together by nonpolar linkages. Some nucleopro- 

 teins migrate as single entities, and the protein cannot be separated from 

 the nucleic acid until it has first been denatured. However, some investi- 

 gators do not regard this as conclusive evidence of a nonsalt type of 

 bonding because the structure of the native protein is quite different from 

 that of the denatured protein, and the configuration may modify the 

 strength of the bonding groups. 



Quantitative data on components 



In Table 6-1 are given examples of nucleoproteins, the kinds of pro- 

 teins contained therein, and the proportion of protein to nucleic acid. 

 Histones and protamines are the common type, but lipoproteins occur 

 frequently in the nucleoproteins of animal tissues. Chromosomes seem to 

 contain two kinds of nucleoprotein, histone and nonhistone types. 

 Mirsky, from whose papers these data are taken, differentiates the two 

 types on the basis of the insolubility of the nonhistone protein in 

 HgS04-H2S04 solution (histone is soluble) and its greater tryptophan 

 content (nonhistone contains 1.36 per cent and histone only 0.14 per 

 cent) . 



Nucleolipoprotein, containing lipoprotein in combination with nucleic 

 acid, indicates a protein having two prosthetic groups, lipide and nucleic 

 acid. Several viruses, e.g., vaccinia virus, have been found to be nucleo- 

 lipoprotein complexes. 



The nucleic acid portion of the nucleoproteins may range from a small 

 fraction, 5 per cent, to m-ore than half of the total. The desoxyribo- 

 nucleic acid (DNA) seems to make up a larger percentage of the nucleo- 

 protein than the ribose form (RNA). Both types of nucleic acid often 

 occur in the same cell. In chromosomes the DNA type predominates, 

 but in yeast cells the RNA form is in excess. 



