3© M. H. F. WILKINS 



molecules have a DNA type structure because other types of double- 

 helix structure formed by synthetic polyribonucleotides [2] give recogniz- 

 able and distinctly different patterns. Moreover the molar proportion of 

 adenine and uracil and of guanine and cytosine are almost equal in this 

 RNA. Mr. W. Fuller has modified the DNA structure and built a mole- 

 cular model of RNA. The hydroxyl group of the ribose is accommodated 

 in the structure by means of various slight distortions. The molecule is 

 stabilized by a hydrogen bond between the hydroxyl oxygen atom and an 

 atom of the adjacent phosphate group. 



This type of structure appears to hold also for ribosomal RNA from 

 Escherichia coli [21]. It has not been found possible to orient the double- 

 helices in this RNA. It appears likely therefore that double helical regions 

 of the molecule are linked together by non-helical parts to form a cluster 

 of short helical regions. This is probably the structure within the ribosomes 

 because the diffraction pattern of ribosomes is the same as that of the RNA 

 mixed with protein. 



It is of interest that earlier preparations of RNA, e.g. from liver, yeast, 

 tobacco mosaic virus, etc., always gave a double helical pattern which, 

 though having a general resemblance to that of DNA, showed distinct 

 differences [22]. It has been noted [21] that this RNA pattern resembles 

 that of a mixture of DNA and double-helix polyriboadenylic acid [2]. 

 Presumably some of these RNA specimens consisted largely of ribosome 

 material. It may be that the earlier methods of preparation caused the 

 RNA molecule to be extended into a filamentous form capable of being 

 oriented and that parts of the molecule had approximately DNA-like base- 

 sequences and that other parts contained more predominantly adenine 

 and formed anti-parallel double-helix structures. This problem is being 

 investigated further. In all cases, however, the length of regular DNA- 

 like regions in RNA is restricted and the diffraction patterns are not well 

 defined. The relation of structure to function in RNA is not yet clear, it 

 has been found, for instance, that the original intact double-helix structure 

 is not required in soluble RNA for amino acid-binding activity to be 

 present [20]. 



Acknowledgments 



In this brief space I will not attempt to acknowledge all those who have 

 contributed to this work but I wish to mention specially Drs. D. A. Marvin 

 and M. Spencer, Mr. W. Fuller, and the University of London Computer 

 Unit. 



References 



1. Josse, J. and Kornberg, A., Fed. Proc. 19, 305 (i960). 



2. Rich A., in "A Symposium on Molecular Biology", ed. R. E. Zirkle, University 

 of Chicago Press (1959). 



