Visualizing transport of the Tat substrate TorA-mCherry into the periplasmic space of <i>E. coli</i> cells.

<p>(<b>A</b>) Fluorescence micrograph of <i>E. coli</i> BL21(DE3) cells expressing TorA-mCherry in the presence of the chromosomally encoded TatABC proteins. TorA-mCherry was expressed from a pET22b+-based plasmid (pPJ3) via the basal level of T7 RNA polymerase, which is synthesized in BL21(DE3) cells under non-inducing conditions and yet yields a sufficiently high fluorescence signal. Rim staining by TorA-mCherry (arrows) can be observed in most of the cells. Bar, 5 µm. (<b>B</b>) Expression of TorA-mCherry in the <i>tatABCD</i> deletion strain BL21(DE3) Δ<i>tat</i>. The Tat-deficient cells are typically arranged in chains of non-separated cells and the fluorescent signal of TorA-mCherry is spread throughout the cytoplasm. (<b>C</b>) Expression of the non-transportable KK-variant of TorA-mCherry in <i>tatABC</i> wild type cells also leads to the retention of the fluorescent substrate in the cytosol.