Identification of functional elements that regulate the glucoamylase-encoding gene (glaB) expressed in solid-state culture of Aspergillus oryzae

Aspergillus oryzae has two glucoamylase-encoding genes, glaA and glaB, whose expressions are distinguished by the type of culture used. The glaB gene is markedly expressed in solid-state culture but is little expressed in submerged culture. In solid-state culture, glaB expression at the transcriptional level is enhanced by low-Aw (water activity), high-temperature, and physical barriers to hyphal extension, as well as by starch. To determine the cis-acting factors in the glaB promoter, deletion analysis of the promoter was done with GUS (beta-glucuronidase) as the reporter. Deletion of the 27 bp from -350 to -324 (Region A) in 1.1 kb of the glaB promoter completely abolished starch, low-Aw, and high-temperature induction. Substitution of the 12-bp GC-rich motif from -335 to -324 (GC-box) resulted in significant loss of starch and low-Aw inductivities. These findings suggest that the GC-box is a cis-element essential for the high-level expression of glaB in solid-state culture.