Fig. 6. Schematic diagram showing the response to physiological ER stress induced by amylolytic enzyme production.

a Expression of amylolytic genes is induced by maltose uptake through MalP, and the unfolded proteins resulting from the synthesis of nascent polypeptides from their mRNAs induce ER stress. b The resulting ER stress activates IreA, leading to HacA activation and RIDD. Thereafter, RIDD and the HacA-mediated UPR and RESS alleviate ER stress. In addition to RIDD and RESS, carbon catabolite repression (CCR) and MalP endocytosis induced by glucose generated from the maltose hydrolysis also contribute to the decrease in amyA/B/C and malP mRNAs. The correctly folded protein is represented by the three-dimensional structural image of α-amylase (PDB ID: 6TAA). The red arrows indicate the activation of transcription factors and CCR.