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7 Transfer RNA: An RNA for All Seasons

Dieter Söll


Long before the existence of an RNA world was accepted, Francis Crick attributed to tRNA enzymatic properties (like a protein) because of its versatility and ability to recognize so many proteins with exquisite specificity. Presumably, this was meant to reflect a well-known property of proteins; conformational flexibility, which is a prerequisite for the manifold recognition characteristics of this small RNA molecule. Even though tRNA alone has been shown to have only marginal enzymatic properties (as discussed below), the many roles of tRNA demand that this molecule assume different conformations to provide diverse points of contact for the selective recognition of many different proteins.

Over the years, tRNA has provided complex challenges in different experimental areas. For biophysicists it provided the first high-resolution X-ray crystal structure of an RNA (Kim et al. 1974; Robertus et al. 1974) and of an RNA:protein complex (Rould et al. 1989), whereas it challenged biochemists to achieve the first sequence determination of an RNA molecule (Holley et al. 1965). For chemists it afforded the first illustration of synthesis of a gene that was biologically active (Ryan et al. 1979), whereas informational suppression acquainted geneticists with tRNA and led them to discover basic principles of protein biosynthesis and the genetic code (for review, see Garen 1968; Steege and Söll 1979). Molecular biologists used the highly specific interaction of tRNAs with aminoacyl-tRNA synthetases to define principles of protein:RNA interaction (for review, see Pallanck and Schulman 1992), whereas molecular archaeologists found tRNA molecules useful in establishing evolutionary relationships of...

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