Figure 6.

Oregon Green maleimide labels cytoplasmic proteins. OGM labeling and subsequent immunoprecipitation were performed as described in Section “Materials and Methods” with the following strains: cGroEL (W3110 expressing chromosomally encoded GroEL) and pTonB L3C ΔTMD (KP1344/pKP544). Samples of cells were also lysed by passage through a French pressure cell and labeled in vitro; these served as a standard for 100% labeling. l-Arabinose was added to induce expression of TonB L3C ΔTMD (0.002%). Proteins were also harvested by treatment with TCA to serve as a total protein control. Samples were divided and resolved on 11% SDS-polyacrylamide gels and immunoblotted with anti-TonB or anti-GroEL antibodies for half of the samples and with anti-OGM antibodies for the other half. Positions of TonB L3C ΔTMD and GroEL are indicated. Molecular mass standards are shown in the center. Abbreviation: IP, immunoprecipitation.