FIG. 4.

Yop delivery to eukaryotic cells. Yop translocation was measured by assessing delivery to and phosphorylation of ELK-tagged YopE from Y. pestis KIM5 and derivative strains in HEp-2 (A) and THP-1 (B) cells. Infected cells were harvested at 2, 4, and 8 postinoculation, and extracts were analyzed by SDS-PAGE and Western blotting, using anti-phospho-ELK and anti-ELK antibodies. Extracts were also tested by Western blotting for Ail (C), Pla (D), and Psa (E) expression from an IPTG-inducible plasmid under various growth conditions over 8 h. A KIM5 ΔyopB strain (lacking a component of the Yop translocation apparatus) was included as a negative control. Δ3 denotes KIM5 Δail Δpla ΔpsaA.