Rheostatic Control of Protein Expression Using Tuner Cells

We assessed the ability of two strains of Escherichia coli, BL21 (DE3) and Tuner (DE3), to express a variant of the B1 domain of protein G, which forms a side-by-side dimer, by using fluorine-labeling and ¹⁹F nuclear magnetic resonance spectroscopy. BL21 cells express the protein in a binary, all-or-none, manner, where more cells express the protein at a high level with an increasing inducer concentration. Tuner cells express the protein in a rheostatic manner, where expression increases across all cells with an increasing inducer concentration.