Construction of an α-Amylase/Glucoamylase Fusion Gene and Its Expression in Saccharomyces cerevisiae

A fusion gene which encoded a polypeptide comprised of 1116 amino acids was constructed using the α-amylase and glucoamylase cDNAs of Aspergillus shirousamii. When the fusion gene was expressed in Saccharomyces cerevisiae using a yeast expression plasmid under the control of the yeast ADH1 promoter, a bifunctional fusion protein (145 kDa) having both α-amylase and glucoamylase activities was secreted into the culture medium. The fusion protein had higher raw-starch-digesting activity than those of the original α-amylase and glucoamylase, and adsorbed onto raw starch like the glucoamylase. It was suggested that the characteristics are a result of the raw-starch-affinity site in the glucoamylase domain of the fusion protein.