The formation of diselenide bridges in proteins by incorporation of selenocysteine residues : biosynthesis and characterization of (Se)2-thioredoxin

A system was devised which allows the efficient substitution of cysteine residues in a protein by selenocysteine. It involves overexpression of the respective gene with the aid of the T7 promotor/polymerase system in a cysteine auxotrophic strain. The induction of the T7 polymerase formation was performed in cysteine-supplemented medium followed by wash-out of the cysteine and production of the desired gene product in the presence of selenocysteine. The system was applied to substitute the two cysteine residues in Escherichia coli thioredoxin