INTRODUCTION 7 



sented another important step. All these techniques were instrumental in 

 the development of current conceptions of nucleic acid structure [Chapters 

 10-12] and helpful in the rapid advance in synthetic procedures for the 

 preparation of nucleic acid constituents [Chapter 4]. 



It has now become abundantly clear that the names pentose nucleic acid 

 and deoxypentose nucleic acid are generic terms indicating groups of com- 

 pounds of similar composition. Chargaff and his colleagues*'^ were the first 

 to show that there are many nucleic acids differing in composition as regards 

 molar proportions of bases according to the biological source of the material 

 from which they are derived. There is even evidence of heterogeneity within 

 the cell, for the pentose nucleic acids of the cytoplasm appear to differ 

 slightly from those of the nucleus in the same tissue [Chapter 11] while the 

 deoxypentose nucleic acids of the nuclei of a single cell type have been sepa- 

 rated into fractions of different molar composition [Chapter 10]. 



The pentose sugar has been identified as ribose in the pentose nucleic acid 

 of yeast^'* and of liver*^ and has been shown to be chromatographically iden- 

 tical with ribose in the nucleic acids from a large number of other sources 

 [Chapter 11]. Consequently, such nucleic acids are frequently referred to as 

 ribonucleic acids (RNA) instead of pentose nucleic acids (PNA). Since 

 there is no evidence of the presence of any other pentose sugar, both terms 

 are legitimate, but for the sake of uniformity the contraction PNA will be 

 used in this book. 



The sugar in thymus deoxypentose nucleic acid has been conclusively 

 proved to be D-2-deoxyribose^^ and the sugars in the corresponding nuclear 

 nucleic acids from a large number of other tissues have been shown to be 

 chromatographically identical with it [Chapter 10]. Consequently, these nu- 

 cleic acids are frequently referred to as deoxyribonucleic acids; but, whether 

 they be called deoxypentose nucleic acids or deoxyribonucleic acids, the 

 contraction DNA is conveniently and frequently used for both names. 



III. Previous Literature 



No major treatises on the chemistry of nucleic acids have appeared since 

 those of Jones," Feulgen,'- and Levene,'' nor has the biochemistry of nucleic 



" R. Vendrely, Bull. soc. Chim. biol. 32, 427 (1950). 



" F. Schlenk, Advances in Enzymol. 9, 455 (1949). 



'' Nucleic acid, Symposia Soc. Exptl. Biol. 1 (1947). 



''* Nucleic acids and nucleoproteins, Cold Spring Harbor Symposia Quant. Biol. 12 



(1947). 

 '^Symposium on the biochemistry of nucleic acids, /. Cellular Comp. Physiol. 38, 



suppl. 1 (1951). 

 '^ The chemistry and phj-siology of the nucleus, Exptl. Cell Research Suppl. 2 (1952). 

 " P. Boulanger and J. Montreuil, Bull. soc. chim. France, 1952, 844. 

 78 A. E. Mirsky, Sci. American 188, 47 (1953). 



