A genomic DNA encoding a second thioredoxin (TRX2) was isolated from the chromosomal DNA of the fission yeast Schizosaccharomyces pombe. The cloned sequence contains 1823 bp and encodes a protein of 121 amino acids. It has extra N-terminal 17 amino acid residues compared to previously identified thioredoxin (TRX1), which are positively charged and hydrophobic amino acids. The additional N-terminal region contains a plausible prepeptidase cleavage site, indicating that the TRX2 protein exists in mitochondria. The cloned TRX2 gene produced functional TRX estimated with insulin reduction assay. The upstream region of the TRX2 gene was fused into the promoterless beta-galactosidase gene of the shuttle vector YEp357R. The 782 bp sequence in the region further upstream of the TRX2 gene was found to be inhibitory in its expression. Synthesis of beta-galactosidase from the fusion plasmid pYFX135-HRL was enhanced by the addition of aluminum chloride and ferrous chloride, indicating that the TRX2 protein is involved in stress response.