Crystal structure of a eukaryotic initiator tRNA

Abstract

OUR understanding of the molecular structure–function relationship in tRNA rests mainly on three types of information. First, on the common sequence patterns which have emerged from careful examination of many primary structures^1–3; second, a wide variety of spectral and other physical and chemical results must be accounted for by the molecular structure^4–6; and third, there is the detailed image of the yeast tRNA^Phe molecule independently determined and refined from two different—albeit similar—crystal forms^7–10. It is also clear, however, that the molecular model deduced from the yeast tRNA^phe crystal structure cannot be easily reconciled with all structural requirements for function and is best considered a well-defined and stable canonical form of tRNA which is packed in an unusually well-ordered way in specific crystal lattices. Notwithstanding the enormous value of this canonical form in explaining the basic architectural features of tRNA, it is clearly important to image other crystalline tRNAs; particularly tRNAs that exhibit different functions (such as, initiators) or have significantly different covalent structures (for example, class III tRNAs)¹ or those that crystallise in different solvent conditions. We report here the initial results of the crystal structure determination of a eukaryotic initiator tRNA crystallised from a highly polar aqueous solvent^11,12. Its architecture is essentially the same as crystalline yeast tRNA^phe, except for a small but significant difference in the position of the anticodon arm.