332 ERWIN CHARGAFF 



ployed, in order to suppress nuclease activity. ^''^■^^^ Nucleic acids from 

 acid-fast bacteria have been isolated by extraction with solutions of low 

 electrolyte concentration, ^^'^^ with salt and urea solutions,^" and with 

 alkali."^ The latter procedure, which has also been applied to E. coli,^*^ 

 degrades, of course, the nucleic acids, though it is effective in removing 

 pentose nucleic acid. The deoxy pentose nucleic acid of Sarcina lutea has 

 also been described,'''*'^'' as have the nucleic acids from two rickettsiae: 

 R. prowazeki and R. hurneti}^^ 



Very little is known about the preparation of deoxy pentose nucleic acids 

 from viruses and even less about the physical state in which the often very 

 robust isolation procedures have left them. Following observations on the 

 behavior of plant viruses,"^ extraction of bacteriophages with urea solu- 

 tions has been used in several instances.^*" '^^^ A milder method, in which 

 the bacteriophage is broken by being passed through a colloid mill, thus 

 producing what has unfortunately been called a "phage grindate," has been 

 outlined recently. ^^^ In other cases, the polyhedral and capsule viruses of 

 insects, the composition of the deoxypentose nucleic acids was deter- 

 mined by the hydrolysis with HCIO4 '^' of the total virus preparations.^" 



h. Removal of Pentose Nucleic Acid and of Other Impurities 



Pentose nucleic acid is in many respects the most troublesome contami- 

 nant of deoxypentose nucleic acid preparations. Its presence vitiates spec- 

 troscopic measurements and makes impossible the analytical characteriza- 

 tion of the specimens. I am listing here some of the procedures that have 

 been employed for the removal of pentose nucleic acid. I. Separation by 

 electrophoresis: this mild, but laborious and wasteful, method has been 

 applied in several instances.^* '^^'^^ II. Fractionation by way of the calcium 

 salts :*^'^^^ the separation will, however, be far from complete. III. Purifica- 

 tion by treatment with crystalline ribonuclease:^^'^'^ this does not ensure 

 the complete removal of the pentose nucleic acid, which may leave behind 



''" E. Chargaff, S. Zamenhof, G. Brawerman, and L. Kerin, J. Am. Chem. Soc. 72, 



3825 (1950). 

 '■" S. Zamenhof, G. Brawerman, and E. Chargaff, Biochim. et Biophys. Acta 9, 402 



(1952). 

 ^** O. Snellman and G. Widstrom, Arkiv. Kemi, Mineral. Geol. 19A, No. 31 (1945). 

 1" A. S. Jones, Biochim. et Biophys. Acta 10, 607 (1953). 

 >« J. D. Smith and G. R. Wyatt, Biochem. J .iQ, 144 (1951). 



'" S. K. Dutta, A. S. Jones, and M. Stacey, Biochim. et Biophys. Acta 10, 613 (1953). 

 '« G. R. Wyatt and S. S. Cohen, Nature 170, 846 (1952). 

 '^' F. C. Bawden and N. W. Pirie, Biochem. J. 34, 1258 (1940). 

 'SO S. S. Cohen, Cold Spring Harbor Symposia Quant. Biol. 12, 35 (1947). 

 '5' G. R. Wyatt and S. S. Cohen, Biochem. J. 56, 774 (1953). 

 1" A. Siegei and S. J. Singer, Biochim. et Biophys. Acta 10, 311 (1953). 

 •" A. Marshak and H. J. Vogel, J. Biol. Chem. 189, 597 (1951). 

 1" G. R. Wyatt, J. Gen. Physiol. 36, 201 (1952). 



