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How Transfer RNA May Move Inside the Ribosome

Alexander Rich


It has been known for many years that transfer RNA (tRNA) is the molecule which carries amino acids into the ribosome and upon which the growing polypeptide chain is assembled. The broad outlines of tRNA and ribosomal participation in protein synthesis are known: tRNA molecules are sequentially lined up in the ribosome through a specific interaction of their anticodon triplets with the codon triplets on the messenger RNA (mRNA) strand and, in this manner, the sequence information encoded in the polynucleotides of mRNA is translated into an individual polypeptide chain. This takes place through a stepwise assembly of amino acids to yield the sequence specificity in proteins. Although this information is generally understood in outline, we do not know in detail how this process occurs. A detailed understanding of a chemical process of necessity requires structural information. The central organelle in this assembly process is the ribosome, and although we have some information concerning its assembly and structure, we do not as yet have a three-dimensional understanding of its structure. However, there has been progress in understanding the three-dimensional structure of tRNA. We have reported the three-dimensional structure of yeast phenylalanine tRNA at a resolution of 5.5 Å (Kim et al. 1972) and 4.0 Å (Kim et al. 1973). More recently we have completed the analysis at a resolution of 3.0 Å (Suddath et al. 1974), which makes it possible to ascertain many details in the folding of the molecule and the positioning of its various components. This naturally...

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