408 MAHLON B. HOAGLAND 



from the particles. Such a mechanism would be a convenient way of deriv- 

 ing the exact proportion of transfer RNA molecules required to react with 

 the amino acids required for the synthesis of the protein that particular 

 ribosome is making. However, since transfer RNA alone appears to con- 

 tain no sequence information, only information permitting recognition of 

 amino acids, some other synthetic mechanism for producing the twenty or 

 so transfer RNA molecules, could be used. It is clear, for example, that the 

 enzymes which attach the terminal grouping of nucleotides to transfer 

 RNA reside in the soluble phase and perhaps other enzymes can synthesize 

 the proper nucleotide sequences specific for the amino acids. Or alterna- 

 tively, such synthesis might occur in the nucleus. 



However these matters may be, the understanding of the mechanism of 

 synthesis of transfer RNA and ribosomal RNA is clearly of very basic im- 

 portance to the unraveling of the cellular mechanism by which the genetic 

 information in DNA is translated into the specific proteins of the living 

 organism. 



Acknowledgment 



I should like to express my thanks to my colleagues Dr. Zamecnik, Dr. Stephenson, 

 and Dr. Loftfield for helpful criticism during the preparation of this chapter. I am 

 also in debt to many colleagues who permitted me to read their manuscripts before 

 publication. 



