Nucleotide sequence and expression of alpha-glucosidase-encoding gene (agdA) from Aspergillus oryzae

We have isolated an alpha-glucosidase(AGL)-encoding gene (agdA) from Aspergillus oryzae by heterologous hybridization using the corresponding Aspergillus niger gene as a probe. Southern hybridization analysis showed that the agdA gene is on a 5.0-kb ScaI fragment and there is a single copy in the A. oryzae chromosome. Comparison with the A. niger agdA gene indicated that the agdA gene contains three putative introns from 52 to 59 nucleotides long, and that it encodes 985 amino acid residues. The deduced amino acid sequence of A. oryzae AGL is 78% homologous with the A. niger AGL. The high degree of homology with the amino acid sequence bordering the putative catalytic residue of a number of AGL enzymes, and this enzyme suggests that Asp492 is a catalytic residue of A. oryzae AGL. The cloned gene was functional. Transformants of A. oryzae containing multiple copies of the cloned agdA gene showed a 6-16 fold increase in AGL activity. Like the Taka-amylase A and glucoamylase genes of A. oryzae, expression of the agdA gene was induced when maltose was provided as a carbon source, but expression was not induced by glucose. This result suggested that cis-element(s) involved in maltose induction may be also present in the agdA promoter region.