The DNA of the gene complementing a PAPS-reductase-deficient strain of Escherichia coli was sequenced. The N-terminal amino acid sequence of the purified PAPS-reductase confirmed that cys H is the structural gene for this enzyme. The open reading frame extends 732 bases and encodes for a peptide of M r = 27927. The gene product is functionally active when supplemented with thioredoxin and immunologically related with the wild type enzyme.
