Cloning and nucleotide sequencing of L-lactate dehydrogenase gene from Streptococcus thermophilus M-192

The gene encoding L-lactate dehydrogenase (LDH) was cloned from an industrial dairy strain of Streptococcus thermophilus M-192 using a synthetic oligonucleotide probe based on the N-terminal amino acid sequence of the purified enzyme, and its nucleotide sequence was determined. The enzyme was deduced to have 328 amino acid residues with a molecular weight of 35,428 and found to have high sequence similarity to LDHs from other lactic acid bacteria (89.0% to Streptococcus mutans, 76.3% to Lactococcus lactis subsp. lactis, 67% to Lactobacillus casei, and 60% to Lactobacillus plantarum). The gene contained a promoter-like sequence similar to the Escherichia coli promoter consensus, and expression of the S. thermophilus LDH gene was observed in E. coli cells.