1962 M. H. F. WILKINS 



-. V 



Fig. 10. Comparison of the X-ray diffraction patterns of fibres of DNA in the A 

 configuration (left) and transfer RNA {right). The general distribution of intensity is 

 very similar in both patterns, but the positions of the sharp crystalline reflections differ 

 because the molecular packing in the crystals is different in the two cases. (Photograph 

 with W. Fuller and M. Spencer; RNA by G. L. Brown.) 



In early work, many RNA preparations were very heterogeneous. We 

 thought that the much more homogeneous plant virus RNA might give 

 better patterns, but this was not so. However, when preparations of ribo- 

 somal RNA and « soluble » RNA became available, we felt the prospects of 

 structure analysis were improved. We decided to concentrate on « soluble » 

 RNA largely because Geoffrey Brown in our laboratory was preparing large 

 quantities of a highly purified transfer RNA component of soluble RNA for 

 his physical and chemical studies, and because he was fractionating it into 

 various transfer RNA's specific for incorporation of particular amino acids 

 into proteins. This RNA was attractive for other reasons : the molecule was 



s-51 



