RNA CODEWORDS AND PROTEIN SYNTHESIS, III. ON THE NUCLEOTIDE SEQUENCE OF A CYSTEINE AND A LEUCINE RNA CODEWORD

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Abstract
The minimum proportions of degenerate species of sRNA corresponding to one amino acid have been estimated by directing sRNA binding to ribosomes with poly-nucleotides. Poly UG and poly UC stimulated the stable binding of approximately 2 and 6 per cent of unfractionated C14-leucine-sRNA, respectively. The binding of purified C14- leucine- sRNA fraction II to ribosomes was stimulated by the trinucleotide UpUpg and by poly UG, but not by UpGpU, GpUpU, or dinucleotides. UpUpG had no effect upon the binding of two other C14-leucine-sRNA fractions. Binding of s35-cysteine-sRNA to ribosomes was directed by UpGpU, but not other tri- or dinucleotide sequence isomers. The nucleotide sequence UpGpU was suggested for a cysteine RNA codeword, and the sequence UpUpG for a leucine RNA codeword corresponding to leucine-sRNA fraction II.