A 6955-bp sequence of a PstI-HindIII DNA fragment containing the manganese-superoxide dismutase (MnSOD) gene of Thermus aquaticus YT-1 was determined. The gene (sod) encoded a polypeptide consisting of 204 amino acid residues (the mature enzyme without the initiation methionine) with a calculated Mr of 22,773. The deduced amino acid sequence of the sod gene showed 92% identity to that of Thermus thermophilus HB8 determined chemically. The sod gene was well expressed in Escherichia coli and a heat-stable active enzyme was produced. An open reading frame encoding fumarase was found 91bp upstream of the MnSOD gene in tandem form. The fum gene encoded a polypeptide consisting of 466 amino acid residues with a calculated M-r of 50,950. The deduced amino acid sequence of the fum gene product has similarity to that of the fumC of E. coli (57% identity), suggesting that this gene encodes a class II type fumarase.