FIG. 2.

Y. pestis is contact activated for secretion and targeting but not contact induced for expression of LcrV and YopE. HeLa cells were infected with Y. pestis KIM8-3002 for 2 h at an MOI of 5, or an equal number of yersiniae were incubated in RPMI without HeLa cells. The total proteins harvested from each well were recovered by TCA precipitation and analyzed in serial twofold dilutions by immunoblotting. In panel A, the blot was probed with a mixture of antibodies to LcrV and YopE; in panel B, a polyclonal anti-Yersinia antibody was used. Proteins were visualized by probing immunoblots with IgG coupled to horseradish peroxidase followed by ECL detection (A) or with alkaline phosphatase-coupled IgG followed by development with NBT-BCIP (B). Fold dilutions of the samples are given above the lanes.