Molecular Cloning and Characterization of a Transcriptional Activator Gene, amyR, Involved in the Amylolytic Gene Expression in Aspergillus oryzae

Abstract

A gene, designated amyR, coding for a transcriptional activator involved in amylolytic gene expression has been cloned from Aspergillus oryzae by screening for a clone that enabled to reverse the reduced expression of the α-amylase gene (amyB) promoter. amyR encodes 604 amino acid residues of a putative DNA-binding protein carrying a zinc binuclear cluster motif (Zn(II)₂Cys₆) belonging to the GAL4 family of transcription factors. The amyR gene disruptants showed a significant restricted growth on starch medium and produced little of the amylolytic enzymes including α-amylase and glucoamylase compared with a non-disruptant, indicating that amyR is a transcriptional activator gene involved in starch/maltose-induced efficient expression of the amylolytic genes in A. oryzae. In addition, sequencing analysis found that amyR, agdA (encoding α-glucosidase), and amyA (encoding α-amylase), are clustered on a 12-kb DNA fragment of the largest chromosome in A. oryzae, and that amyR is about 1.5 kb upstream of agdA and transcribed in the opposite direction. Furthermore, transcriptional analysis revealed that the amyR gene was expressed in the presence of glucose comparable to the level in the presence of maltose, while the amylolytic genes were transcribed at high levels only in the presence of maltose.

• Aspergillus oryzae
• transcriptional activator
• amylolytic enzyme
• zinc finger motif
• gene cluster