FIG. 1.

Dam overproducer Y. pseudotuberculosis strains ectopically secrete Yops. Proteins were isolated from culture supernatants from wild-type (WT) and Dam overproducer (OP) Yersinia strains grown at the indicated temperatures in the presence (+Ca²⁺) or absence (−Ca²⁺) of calcium according to the method of Forsberg et al. (11). Cells were separated from the culture supernatant by centrifugation, supernatant proteins were precipitated with ammonium sulfate, and proteins were analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and visualized by Coomassie blue staining. Yops were identified according to the method of Hakansson et al. (16). Numbers refer to molecular weight standards (in thousands).