Recombinant product and repressor production. (A) Fate of recombinant proteins expressed in E. coli. After translation the folding intermediates of the protein can reach their native conformation, be deposited in soluble aggregates, or reach a misfolded state. Both native protein and soluble aggregates can be deposited in insoluble inclusions, from where polypeptides can be targeted for degradation. (B) Total amount of GFP (according to SDS PAGE) produced after 8 h of growth in different clones. Expression system without the use of pNF_TetR was set as internal reference (GFP content = 1) (C) Percentage of soluble GFP produced as a fraction of the total GFP. Insert in upper left corner depicts the difference in non-GFP producing and GFP producing cells in the soluble (S) and insoluble (IS) fraction. (D) Relative values of TetR protein in the soluble protein fraction according to Western Blot analysis. The mutant with the lowest TetR production (mFB-2) was set as reference to 1. No FB - no feedback plasmid used for GFP expression; WT FB-1 - set 1 of WT promoter clones; WT FB-2 - set 2 of wild type promoter clones (See Additional file 1: Figure S1 for further information); mFB-1 - mutant stress promoter 3_1 with strong RBS; mFB-2 mutant stress promoter and weak RBS. Values represent averages +/- standard error of the mean.