Nucleotide Sequences of Rat-Liver Serine tRNA. Structure of Serine tRNA3 and Partial Nucleotide Sequences of Serine tRNA2a

Abstract

The purification of serine tRNA3 from rat liver and the identification of the products of digestion with pancreatic and T1 ribonucleases are described. The following primary sequence was determined by nucleotide overlaps and by analysis of a partial T1-ribonuclease digest: pG-A-C-G-A-G-G-U-G-G-C-ac4C-G-A-G-hU-Gm-G-hU-hU-A-A-G -G-C-m22G-A-Ψ-G-G-A-m3C-U-G-C-U -mt6A-A-Ψ-C-C-A-U-Um-G-Ψ-G-C-U-m3 -C-U-G-C-A-C-G-m5C-G-U-G-G-G-T-Ψ-C-G-m1A-A-U-C-C-C-A-U-C-C-U-C-G-U-C-G-C-C-A-OH where mt6A =N-[(9-β-d-ribofuranosyl-purine-6-yl)-N -methyl-carbamoyl]threonine. This tRNA, which recognizes the codons AGC and AGU, can be arranged in the classical cloverleaf structure. Its length of 85 nucleotides is the same as that of other eukaryotic serine tRNA species so far sequenced. The analysis of a T1-ribonuclease digest of a further serine tRNA fraction, designated serine tRNA2, is also described. This fraction consists mainly of a species coding for UCG. From these data we can tentatively derive part of the structure of this molecule. The sequences reported here are compared to those of known serine tRNAs from Escherichia coli, yeast and rat liver. The possible site of synthetase recognition of the isoacceptor serine tRNAs is discussed.