FIG. 4.

Intracellular localization of ExoU proteins with MLD substitutions. ExoU proteins containing an N-terminal GFP tag were expressed in HeLa cells by transient transfection. At 20 h posttransfection, cells were fixed, treated with Hoechst stain to label nuclei (blue), and visualized by fluorescence microscopy. All constructs except GFP-ExoU-LS608 contain the S142A substitution, which eliminates cytotoxicity, so that proteins could be visualized. Representative images are shown. S142A, GFP-ExoU-S142A; LS608, GFP-ExoU-LS608; S+I609N, GFP-ExoU-S142A-I609N, etc.