THE CHEMICAL NATURE OF THE RNA-AMINO ACID COMPOUND FORMED BY AMINO ACID-ACTIVATING ENZYMES

Recently, Hecht et al.2 showed that the acceptor activity of liver RNA required a cific terminal sequence of nucleotides, i.e., adenylyl 5'-3'-cytidylyl-5'-3'idylyl-5'-3'-RNA (RNApCpCpA13). It seemed likely that this grouping proes either the point of attachment of amino acids to the RNA or that this terlal sequence is required for the binding of the RNA to the activating enzyme. a experiments described in the present report were designed to distinguish be,en these two possibilities. )ur results show that the leucine-, valine-, and methionine-activating enzymes c the respective amino acids to the RNA through the 2'or 3'-hydroxyl group he ribose of the terminal nucleotide bearing the unesterified 3'-hydroxyl group. have identified the terminal nucleotide of the chain which accepts leucine as nylic acid by isolating leucyl-2'or 3'-adenosine from RNase digests of leucylA. From the behavior of the bound amino acids to treatment with hydroxyla-e,6 7, 14 we have inferred that the linkage is an acyl ester. Based on the present inoza, W., Nature, 181,958 (1958). raenkel-Conrat, H., B. Singer, and R. C. Williams, Bioch m. et Biophys. Acta, 25, 87 (1957). raenkel-Conrat, H., Cellular Biology, Nucleic Acids and Viruses, Spec. Publ. N. Y. Acad. 5y, 217 (1957). raenkel-Conrat, H., Trans. F raday Soc. (in press). our-el, A., and C. A. D kker (personal commu ication).