FIG. 4.

Protein dimerization mediated by the VacA N-terminal region. E. coli strains MM39, MM39 pccGpA-wt, MM39 pccGpA-G83I, MM39 pccVacA-wt, and MM39 pccVacA-G14A were cultured in Luria-Bertani medium to an optical density of approximately 0.35 at 600 nm. CAT activity from each strain was quantified using the Quan-T-CAT assay system (Amersham-Pharmacia Biotech). Results represent the mean and standard deviation from triplicate cultures. MM39 pccVacA-G14A produced significantly less CAT activity than MM39 pccVacA-wt (Student's t test, P < 0.003), and MM39 pccGpA-G83I produced significantly less CAT activity than MM39 pccGpA-wt (Student's t test; P < 0.0002).