FIG. 4.
Determination of intracellular concentrations of σA, σB, and E in wild-type B. subtilis during ethanol stress. Extracts were prepared from cells before and after exposure to ethanol (EtOH) stress. Dilutions of purified standard proteins (His6-σA, His6-σB, and E) and of cell extracts were used for Western blotting and immunodetection with σA-, σB-, and E-specific antibodies (A). Quantification of intracellular σA, σB, and E was performed as described in Materials and Methods. Standard curves were generated by using dilutions of purified standard proteins (B). The intracellular concentrations of σA, σB, and E were then determined (C). The error bars indicate the standard error of the mean. BLU, Boehringer light units.