CHEMICAL PATHWAYS 



105 



nucleotide, and accordingly both 2' and 3' positions of the ribose in the 

 terminal adenylic nucleotide are free. This is established by periodate 

 oxidizability of the terminal adenylic residue, and by the fact that when i^C- 

 labelled ATP is used as a source of terminal adenylic acid, most of the label 

 in the alkali hydrolysate is recovered as adenosine. 



CHg 



Cytosine 



Cytosine 



Adenine 



Cytosine 



Cytosine 



Adenine 



OH OH 



Fig. 28. Terminal sequence of soluble transfer RNA with and without 

 attached amino acid. 



Prolonged incubation of soluble RNA removes the terminal nucleotides, 

 and fixation of amino acids is possible only after the reformation of the 

 terminal cytidyl-cytidyl adenosine (C-C-A) sequence (Hecht et aL, 1958, 

 1959). Singer and Cantoni (1960), on the other hand, provided evidence that 



