37. NUCLEIC ACID AND PROTEIN SYNTHESIS 377 



such investigations was, of course, to elucidate the mechanism of RNA 

 synthesis. It has come about, however, that much of this work has tended 

 to illuminate protein synthesis, and has made questionable some of the 

 earlier conclusions about RNA synthesis. This paradox is due to the fact 

 that a large amount of the turnover of base precursors in sRNA has been of 

 a very special and limited sort : the turnover of certain nucleotide end groups 

 of sRNA. This phenomenon seems to be related to the preparation of the 

 end groups of sRNA for amino acid attachment, and not directly to the 

 synthesis of RNA itself. 



It was shown by Goldwasser 145 that homogenates of pigeon pancreas in- 

 corporated AMP-C 14 into RNA and that the adenylic acid-2',3'-C 14 was 

 recovered on alkaline hydrolysis. If the AMP were labeled instead with 

 P 32 , alkaline hydrolysis led to the appearance of P 32 in the 2 '3 '-nucleotides 

 of all four bases suggesting that the AMP was randomly distributed in the 

 molecules. 



Other studies on nucleotide incorporation 146 ' 148 showed similar incorpora- 

 tions into RNA fractions of an unspecified kind, either as to level of phos- 

 phorylation of the immediate precursor or the site of incorporation into the 

 RNA molecule. The earliest indication that there was a specific site of in- 

 corporation came from the work of Heidelberger et al. U9 who, using AMP 32 , 

 found that diesterase released the incorporated AMP as the 5 '-nucleotide 

 and that the P 32 was associated only with the 2',3'-cytidylic acid fraction 

 on alkaline hydrolysis. This indicated that a special type of AMP incorpora- 

 tion was proceeding in this particular system — one in which the AMP was 

 preferentially linked to cytidine monophosphate (CMP). This system de- 

 pended on conditions of oxidative phosphorylation in which the AMP pre- 

 cursor would have been brought to higher levels of phosphorylation prior 

 to incorporation into RNA. 



A series of investigations of these phenomena in a number of laboratories 

 unfolded the picture of a predominant terminal attachment of adenine 

 nucleotides to the soluble RNA fraction. 135, 15(M54 This was concluded since 

 most of the incorporated adenine was released as the nucleoside on alkaline 



146 E. Goldwasser, J. Am. Chem. Soc. 77, 6083 (1955). 



146 E. Herbert, V. R. Potter, and L. I. Hecht, J. Biol. Chem. 225, 659 (1957). 



147 E. S. Canellakis, Biochim. et Biophys. Acta 23, 217 (1957). 



148 R. Logan, Biochim. et Biophys. Acta 26, 227 (1957). 



149 C. Heidelberger, E. Harbers, K. C. Leibman, Y. Takagi, and V. R. Potter, Bio- 

 chim. et Biophys. Ada 20, 445 (1956). 



150 P. C. Zamecnik, M. L. Stephenson, J. F. Scott, and M. B. Hoagland, Federation 

 Proc. 16, 197 (1957). 



161 A. R. P. Paterson and G. A. LePage, Cancer Research 17, 409 (1957). 



162 E. S. Canellakis, Biochim. et Biophys. Acta 25, 217 (1957). 



153 M. Edmonds and R. Abrams, Biochim. et Biophys. Acta 26, 226 (1957). 

 164 E. Herbert, J. Biol. Chem. 231, 975 (1958). 



