A novel function of Escherichia coli transfer RNA nucleotidyltransferase. Biosynthesis of the C-C-A sequence in a phage T4 transfer RNA precursor.

The biosynthesis of the phage T4-coded proline and serine transfer RNA species proceeds through a precursor RNA containing both tRNA sequences. Neither tRNA sequence in the precursor RNA contains the 3'-terminal C-C-A common to all mature tRNAs. Seidman and McClain ((1975) Proc. Natl. Acad. Sci. U. S. A. 72, 1491-1495) have proposed that the C-C-A sequence is added to serine tRNA while it is still part of the large precursor RNA. In the present work, I show that, in vitro, a purified preparation of Escherichia coli tRNA nucleotidyltransferase (EC 2.7.7.25) accurately synthesized 3'-terminal C-C-A in the serine tRNA portion of the precursor RNA. This result establishes a role of tRNA nucleotidyltransferase in the biosynthesis of the phage T4 serine tRNA. The finding that tRNA nucleotidyltransferase utilizes the large precursor RNA as a substrate represents a novel function of the enzyme.