Streptococcus mutans induces both H₂O₂-forming and H₂O-forming NADH oxidases in the presence of O₂ [M. Higuchi, J. Gen. Microbiol., 130, 1819-1826 (1984)]. In this paper, a nox-1 gene encoding H₂O₂-forming NADH oxidase (NOX-1) from Streptococcus mutans was cloned, and the nucleotides sequenced. The structural gene of nox-1 consisted of 1530 base pairs, which encode a polypeptide consisting of 510 amino acids with a predicted molecular mass of 55, 196 Da. The deduced N-terminal amino acid sequence was consistent with that previously found for the purified NOX-1 protein. The nox-1 gene was expressed in Escherichia coli using its own promoter. Alignment of the amino acid sequence of NOX-1 with those of NADH oxidases from other microorganisms showed identities of 55.6%, 20.8%, 20.3%, and 7.3% for those of Amphibacillus xylanus Ep01, Streptococcusfaecalis 10C1, Thermoanaerobium brockii Rt8. G4, and Thermus thermophilus HB8, respectively.

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