I962 M.H. F. WILKINS 



single crystals of DN A could be obtained, the intensity data would be ad- 

 equate for precise determination of all atomic positions in DNA (apart from 

 the non-periodic base sequence). 



We are investigating the possibility of obtaining single crystals of DNA, 

 but the more exciting problem is to obtain single crystals of transfer RNA 

 with crystalline perfection equal to that of DNA, and thereby analyse base 

 sequence. At present, the RNA crystals are much less perfect than those of 

 DNA. However, most of our experiments have been made with RNA that 

 is a mixture of RNA's specific for different amino acids. We have seldom 

 used RNA that is very largely specific for one amino acid only. We hope 

 that good preparations of such RNA may be obtained consisting of one type 

 of molecule only. We might expect such RNA to form crystals as perfect 

 as those of DNA. If so, there should be no obstacle to the direct analysis of 

 the whole structure of the molecule, including the sequence of the bases and 

 the fold at the end of the helix. We may be over-optimistic, but the recent 

 and somewhat unexpected successes of X-ray diffraction analysis in the nu- 

 cleic acid and protein fields, are cause for optimism. 



Acknowledgements 



During the past twelve years, while studying molecular structure of nucleic 

 acids, I have had so much help from so many people that all could not be 

 acknowledged properly here. I must, however, thank the following : 



Sir John Randall, for his long-standing help and encouragement, and for 

 his vision and energy in creating and directing a unique laboratory; 



all my co-workers at various times over the past twelve years; first, 

 Raymond Gosling, Alex Stokes, Bill Seeds, and Herbert Wilson, then Bob 

 Langridge, Clive Hooper, Max Feughelman, Don Marvin, and Geoffrey 

 Zubay ; and at present, Michael Spencer, Watson Fuller, and Struther Arnott, 

 who with much ability, skill and persistence (often through the night) car- 

 ried out the X-ray, molecular model-building, and computing studies; 



my late colleague Rosalind Franklin who, with great ability and expe- 

 rience of X-ray diffraction, so much helped the initial investigations on 

 DNA; 



Leonard Hamilton for his constant encouragement and friendly cooper- 

 ation, and for supplying us with high-quality DNA isolated in many forms 

 and from many sources ; Geoffrey Brown for giving me moral and intellec- 



s-57 



