1991 Volume 109 Issue 6 Pages 852-857
A gene (leuB) coding for 3-isopropylmalate dehydrogenase [EC 1.1.1.85] from an extreme thermophile, Thermus aquaticus YT-1 was cloned in Escherichia coli and the nucleotide sequence was determined. It contains an open reading frame of 1, 035 by encoding 344 amino acid residues. The homology with that from T. thermophilus HB8 is 87.0% in nucleotide and 91.3% in amino acid sequences. No overlapped gene was found in the present leuB gene, in contrast to the previous prediction that Thermus leuD gene is overlapped with leuB [Croft et al. (1987) Mol. Gen. Genet. 210, 490-497] . Substitutions in the primary structure which are unique for the thermophile sequences are discussed in relation to the unusual stability of the thermophile dehydrogenase based on amino acid sequence comparison of 9 micro-organisms including thermophiles and mesophiles.