Structure and function of the yeast tRNA ligase gene.

We report here the DNA sequence of the entire coding region of the Saccharomyces cerevisiae tRNA ligase gene. tRNA ligase is one of two enzymes required for tRNA splicing in yeast, and the enzyme is likely a single polypeptide with multiple activities. We find that tRNA ligase is a basic protein of 827 amino acids corresponding to a molecular weight of approximately 95,400. The inferred amino acid sequence for tRNA ligase is not significantly homologous to that of other known proteins of similar activity. In addition to the tRNA ligase reading frame and several other unidentified open reading frames, we have found two open reading frames, ORF1 and ORF2, near the 5'-end of the ligase structural gene. One of these, ORF2, produces a divergent transcript which initiates only 125 nucleotides upstream of the tRNA ligase transcript, and is present in approximately the same relative abundance as the transcript for tRNA ligase.