312 ERWIN CHARGAFF 



tones soluble in isotonic salt solutions. Whether these nucleoproteins occur 

 only in -microorganisms cannot yet be stated. A histone has been claimed 

 to be present in the nucleoprotein fraction of Type III pneumococci.^^ It 

 is not impossible that the protein moiety of these nucleoproteins has a more 

 complicated amino acid composition than have the basic proteins of low 

 molecular weight. Moreover, the existence of similar nucleoproteins in the 

 nuclei of higher organisms cannot be excluded, although complications 

 arising from the contamination of the preparations with cytoplasmic ma- 

 terial may account for some of the results. While nucleoprotamine appears 

 to constitute almost the entire mass of defatted fish sperm nuclei,^^"" many 

 other varieties of nuclei include tryptophan-containing proteins.^'* -^^ ■" The 

 nucleoproteins of some of the animal and bacterial viruses possibly also 

 belong to this class; but, the chemical information available at present is 

 not sufficient for a decision. 



It is quite obvious that we are very far from a meaningful classification 

 of the types of deoxypentose nucleoprotein occurring in cell nuclei, espe- 

 cially with regard to changes in the composition of the protein moiety 

 taking place during development and in the several phases of the mitotic 

 cycle. 



3. Isolation 



Two principal methods, both foreshadowed in the pioneering work of 

 Miescher,* have been used for the preparation of nucleoprotamines and of 

 nucleohistones, i.e., complexes in which the protein partner carries a posi- 

 tive charge. They are based on (a) extraction with solutions of low ionic 

 strength j^*'^*'^" (b) extraction with strong salt solutions.^* "'^ In recent 

 years, the studies of Hammarsten^" and of Mirsky and PoUister^^ were of 

 particular importance in providing the impulse for the isolation of a large 

 number of highly polymerized preparations of deoxypentose nucleic acid. 

 As already has been mentioned, certain bacterial nucleoproteins, which 

 appear to belong to an entirely different type of nucleoprotein, can be ex- 

 tracted with dilute buffers and fractionated by conventional means.^^ 



24 A. E. Mirsky and A. W. Pollister, J. Gen. Physiol. 30, 117 (1946). 

 26 A. W. Pollister and A. E. Mirsky, /. Gen. Physiol. 30, 101 (1946). 



26 K. Felix, H. Fischer, A. Krekels, and R. Mohr, Z. physiol. Chem. 287, 224 (1951). 



27 K. Felix, H. Fischer, A. Krekels, and R. Mohr, Z. physiol. Chem. 289, 10 (1951). 



28 E. Stedman and E. Stedman, Cold Spring Harbor Symposia Quant. Biol. 12, 224 

 (1947). 



29 A. E. Mirsky and H. Ris, J. Gen. Physiol. 31, 1, 7 (1947). 



30 E. Hammarsten, Biochem. Z. 144, 383 (1924). 



3' A. E. Mirsky and A. W. Pollister, Proc. Natl. Acad. Sci. U. S. 28, 344 (1942). 



