The nucleotide sequence of a cDNA coding human threonyl-tRNA synthetase has been determined. The predicted protein sequence is highly homologous to that of the yeast cytoplasmic, yeast mitochondria and Escherichia coli threonyl-tRNA synthetases. In particular, the three structural motifs recently shown to be common to class II aminoacyl-tRNA synthetases are present in the threonyl-tRNA synthetases from all sources. Primer extension and S1 nuclease analyses indicate that transcription initiates approximately 220-230 nucleotides upstream of the putative initiator methionine codon. This region contains a 10-nucleotide interrupted inverted repeat flanked by a 13-nucleotide interrupted direct repeat.