The incorporation of nucleotides into amino acid transfer ribonucleic acid. 3. Thincorporaton of uridylic acid.

An enzyme preparation from rabbit muscle catalyzes the incorporation of uridine monophosphate into the terminal nucleotide sequence of yeast amino acid transfer ribonucleic acid. Reactants are UTP, Mg++, and transfer RNA which has been partially digested with snake venom phosphodiesterase. Some characteristics of the incorporation system are presented. Incorporation of UMP into tranfer RNA rather than into a different species of RNA was shown by a similar chromatographic profile of the RNA fraction labeled with UMP, or with @dine monophosphate, by competition between UMP and CMP for a limited number of sites in the RNA molecule, and by nearest neighbor analysis. The latter indicated that 2 UMP residues cannot be incorporated as neighbors in a manner similar to the subterminal CMP residues in transfer RNA.