16 CHEMICAL SPECIFICITY OF NUCLEIC ACIDS 



TABLE 7 

 COMPOSITION OF YEAST RIBONUCLEIC ACIDS 



(in moles of nitrogenous constituent per mole of P) 



absorption of the pure nucleotides^^' ^^. The very good recoveries 

 of nucleotides obtained in terms of both nucleic acid phosphorus 

 and nitrogen show the cleavage by mild alkali treatment of 

 pentose nucleic acids to be practically quantitative. 



In Procedure 2, the purines are first Uberated by gaseous HCl 

 in dry methanol and the evaporation residue of the reaction 

 mixture is adjusted to pH 13.5 and then treated as in Procedure 1. 

 In this manner, uridylic and cytidylic acids, adenine and guanine 

 are separated and determined on one chromatogram. 



The determinations of free purines and pyrimidines in acid 

 hydrolysates of pentose nucleic acids, following the methods 

 outlined before for the deoxypentose nucleic acids, are listed as 

 Procedure 3. It will be seen that it is mainly uracil which in this 

 procedure escapes quantitative determination. This is due to the 

 extreme refractoriness of uridylic acid to complete hydrolysis by 

 acids, a large portion remaining partially unsplit as the nucleoside 

 uridine. As matters stand now, I consider the values for purines 

 yielded by Procedures 1 and 3 and those for pyrimidines found 

 by Procedures 1 and 2 as quite reliable. 



A survey of the composition of yeast ribonucleic acid is pro- 

 vided in Table 7. Preparations 1 and 2, listed in this table, were 

 commercial preparations that had been purified in our laboratory 

 and had been subjected to dialysis; Preparation 3 was isolated 



