Cloning, nucleotide sequencing, and expression of the β-galactosidase-encoding gene (lacA) from Aspergillus oryzae

lacA coding for β-galactosidase (β-gal) was cloned from the genomic DNA of Aspergillus oryzae RIB40. There were 9 exons in lacA and the coding region of 3,015 bp encoded a protein of 1,005 aa with a deduced molecular mass of 109,898. A. oryzae lacA was highly homologous to fungal βgals, with the highest aa identity of 70.7% to A. niger lacA, and also showed significant identity to acid β-gals belonging to family 35 glycosyl hydrolases. Approximately 10 copies of lacA under control of A. oryzae, glaA promoter were integrated into the chromosome of A. oryzae M-2-3. The recombinant strain expressed more than 700-fold of the β-gal activity as compared to the wild type strain under induction by maltose.