FIG. 6.

Type III injection of YopE into HeLa cells is impaired if a synonymous substitution is introduced into codon 3. (A) Y. enterocolitica LC1 harboring either the plasmid-encoded wild type or the A9C mutant yopE was induced for type III secretion in low-Ca²⁺ medium. Secretion of YopE was measured as described in the legend to Fig. 1. (B) HeLa cell monolayers were infected with LC1 harboring either the plasmid-encoded wild type or the A9C mutant yopE. After 3 h, the medium was removed and separated by centrifugation to yield supernatant (S) and pellet (P) fractions. The monolayer with adherent bacteria was treated with 1% digitonin and separated by centrifugation to yield supernatant (S) and pellet (P) fractions. Protein samples were treated and analyzed as described in the legend to Fig. 1.