The determination of a novel protein structure by X-ray diffraction is seldom straightforward. Three hurdles present themselves (i) the protein must be purified in sufficient quantity to allow crystallization trials, (ii) crystals must be grown to adequate size and must diffract to a resolution that will allow atomic detail to be revealed, and (iii) phases must be determined for the diffracted X-ray beams in order that an initial electron-density map may be calculated.

Technology which makes use of biological materials has advanced dramatically in the last few decades. Production of specific biochemicals by selected microbial strains, the use of enzymes for stereospecific biosynthesis of materials and gene technological production of biologically important macromolecules are a few examples of these developments.

RNA molecules perform a wide variety of biological functions, from enzymic activity to storage and propagation of genetic information.