1962 M.H. I'.WILKINS 



Relation of the Molecular Structure oj RNA to Function 



Molecular model-building shows that the number of nucleotides forming 

 the fold at the end of a transfer RNA molecule must be three or more. In 

 our model, the fold consists of three nucleotides, each with an unpaired base. 

 It might be that this base-triplet is the part of the molecule that attaches to 

 the requisite part of the coding RNA polynucleotide chain that determines 

 the sequence of amino acids in the polypeptide chain of a protein. It is 

 believed that a base-triplet in the coding RNA corresponds to each amino 

 acid. The triplet in the transfer RNA could attach itself specifically to the 

 coding triplet by hydrogen-bonding and formation of base-pairs. It must 

 be emphasized, however, that these ideas are speculative. 



We suppose that part of the transfer RNA molecule interacts specifically 

 with the enzyme that is involved in attaching the amino acid to the RNA; 

 but we do not know how this takes place. Similarly, we know little of the 

 way in which the enzyme involved in DNA replication interacts with DNA, 

 or of other aspects of the mechanics of DNA replication. The presence of 

 complementary base sequences in the transfer RNA molecule, suggests that 

 it might be self-replicating like DNA; but there is at present little evidence 

 to support this idea. The diffraction patterns of virus and ribosome RNA 

 show that these molecules also contain helical regions; the function of these 

 are uncertain too. 



In the case of DNA, the discovery of its molecular structure led imme- 

 diately to the replication hypothesis. This was due to the simplicity of the 

 structure of DNA. It seems that molecular structure and function are in 

 most cases less directly related. Derivation of the helical configuration of 

 RNA molecules is a step towards interpreting RNA function; but more 

 complete structural information, e.g. determination of base sequences, and 

 more knowledge about how the various kinds of RNA interact in the ribo- 

 some, will probably be required before an adequate picture of RNA func- 

 tion emerges. 



The Possibility of Determining the Base Sequence of Transfer RNA by X-ray 



Diffraction Analysis 



Since the biological specificity of nucleic acids appears to be entirely deter- 

 mined by their base sequences in them, determination of these sequences is 

 probably the most fundamental problem in nucleic acid research today. The 



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