Process for producing optically active 4-halo-3-hydroxybutanoate

There are provided a polynucleotide sequence coding for an amino acid sequence capable of preferentially producing (S)-4-bromo-3-hydroxy-butanoate by asymmetrically reducing 4-bromo-3-oxobutanoate, A DNA construct having a promoter in operative linkage with the polynucleotide sequence, a recombinant vector containing the polynucleotide sequence, a transformant, a recombinant vector and the like.