Phenotypes and insert positions of EspP linker mutants.

Constructs are listed in order from N- to C-terminus of the EspP holoprotein. Nomenclature of mutants is according to the insert position of the 5 amino acid linker in the primary sequence of EspP. Mutants designated “a” and “b” represent independent insertions at identical amino acid positions. The resulting phenotype is illustrated as follows: • active, ○ inactive, □ residual activity of ∼10–20%. NA, not applicable because of absent secretion competence.