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 reso-nance spectroscopy. BL21 cells express the protein in a binary, all-or-none, manner where more cells express the protein at a high level with increasing inducer concentration. Tuner™ cells express the protein in a rheostatic manner where expression increases across all cells with increasing inducer concentration.