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The redundance, or degeneracy as it is generally called, of amino acid coding has been deduced from various observations. Holley and his group, 1 by applying countercurrent distribution to the mixture of sRNA's, obtained two or more distinct sRNA peaks for the same amino acid. The use of polynucleotides of fixed composition, introduced by Nirenberg and his group,2 and by Ochoa and collaborators,3 for probing polypeptide synthesis from activated amino acids, has indicated that the same amino acid can respond with polypeptide formation to different polynucleotides. A pronounced redundance was found for leucine, which showed incorporation into polypeptide chains in a system stimulated by poly UC, poly UG, poly UA, or poly U.4-6 The recently observed7 specific coding of one leucine-specific countercurrent peak by poly UC, and the other by poly UG, as well as less pronouncedly by poly U, amplifies these observations by indicating the possibility of a coding difference between the two leucine sRNA fractions. The matching of the activating enzyme of one species with the sRNA from another species has indicated only a partial overlap and qualitative as well as quantitative differences in the sRNA.5 Since a number of observations9-" indicate universality of the code, a differential response to activating enzymes has been interpreted to mean that the affinity of amino acid-specific sRNA, when matching the activating enzyme, may not be due to the coding nucleotide combination. Such a conclusion, however, may need revision, as will be seen from the experiments to be reported here. In expanding on the type of experiments first made by Berg,8 it now appears that a crude E. coli sRNA preparation, that is partially charged with leucine by yeast enzyme, respo ads almost exclusively to poly UC in a similar manner to the countercurrent peak I-sRNA in the experiments of Weisblum et al.,7 while the remainder appears to be coded preferentially by poly UG. Experiments on the question of code universality will also be reported. Methods.-Soluble RNA from E. coli B was prepared by the phenol procedure described by von Ehrenstein and Lipmann.9 Enzyme preparations: E. coli B cells (log phase) were ruptured after the method of Berg.8 The extract was centrifuged twice at 30,000 X g for 30 min in the 9-in. rotor of the Lourdes centrifuge, and at 105,000 X g for 2 hr in the No. 40 rotor of the Spinco. The 105,000 X g supernatant was stored frozen; when thawed, it was passed, just before use, through a Sephadex G-25 column that had been equilibrated with 0.01 Alphosphate-0.005 Al mercaptoethanol buffer pH 7.0. National bakers' yeast was stirred with liquid nitrogen for several minutes. The nitrogen was permitted to evaporate and the ruptured yeast cells were immediately stored at -20'. For 2 min, frozen yeast was blended in a Virtis homogenizer with glass beads and 0.01 Al Tris-0.005 Al1 mercaptoethanol pH 7.5. The extract was centrifuged at 30,000 X g for 30 min, then at ] 05,00() X g for 2 hr. The 105,000 X g supernatant was passed through Sephadex G-25 just before use. Attachment of C14-leucine to sRNVA: The procedure of von Ehrenstein and Lipmann9 was used to attach C'4-leucine to either yeast or E. coli sRNA by enzymes from yeast or E. coli extracts;

CODING PROPERTIES OF E. COLI LEUCYL-sRNA's CHARGED WITH HOMOLOGOUS OR YEAST ACTIVATING ENZYMES