MOLECULAR-CLONING AND NUCLEOTIDE-SEQUENCE OF THE GENE ENCODING A H2O2-FORMING NADH OXIDASE FROM THE EXTREME THERMOPHILIC THERMUS-THERMOPHILUS HB8 AND ITS EXPRESSION IN ESCHERICHIA-COLI

The sequence of the 32 N-terminal amino acids of the NADH oxidase from the extreme thermophile, Thermus thermophilus HB8, was used to synthesize oligonucleotides to probe for the respective gene in a genomic library of T. thermophilus HB8. The gene encoding the NADH oxidase, designated nox was cloned, its nucleotide sequence was determined and found to be colinear with the N-terminal sequence of the enzyme. The molecular mass of 26835 Da, as deduced from the nox gene, agrees with that of the purified NADH oxidase from T. thermophilus HB8 (25000 Da), as estimated by polyacrylamide gel electrophoresis under denaturing conditions. The nox gene was overexpressed in Escherichia coli and a protocol for the rapid purification of the enzyme was developed. The E. coli-borne T. thermophilus HB8 NADH oxidase has properties identical to those of the authentic T. thermophilus HB8 enzyme and possesses a high thermal stability.