X-ray Diffraction Studies of the Secondary Structure of RNA

I shall start by reviewing the background to X-ray diffraction studies of RNAs of all types, and then explain what our present methods can and cannot achieve; to conclude I shall report some work which is in progress on soluble RNA (S-RNA). The methods which we use have developed naturally from those used for many years now in studying the structure of DNA. Diffraction patterns from DNA and from RNA are of the same type, in that they are “fiber diagrams” containing diffraction from many individual crystallites in the specimen; the crystallites are arranged with their long axes parallel to the fiber axis, but are otherwise oriented at random. The pattern obtained is equivalent to that given by a single crystal which is rotated during the exposure; some of these reflections (though not all) are overlapped by reflections from other crystallites. There is also a fading out of reflections...