Fig. 3.
Characterization and application of the malO operator in inducible tuning of promoter strength in B. subtilis. (A) Conceptual diagram of the malO operator employed as an inducible enhancer in modifying promoter strength. Alpha-amylase and human FGF21 served as proteins of interest, and their necessary chaperones, PrsA and DnaK, were selected to help fine-tune protein expression levels of the proteins of interest. The effects of different nucleotide distances between the inserted malO operator and the native promoter PprsA (B) and promoter PhrcA (C) were investigated to determine optimal placement of the operator to promote GFP expression with (I) or without (UI) the inducer maltose. Subsequently, the malO operator with the optimal distance was inserted upstream of the promoters PprsA and PhrcA.