Extracellular protein profiles of ExoY-expressing strains. P. aeruginosa strains (as in Table 1; wt, PA103; exsA, PA103exsA∷Ω; exoU/T, PA103ΔexoUexoT∷Tc; popD, PA103popD∷Ω) were grown to an OD540 between 4.0 and 5.0, and extracellular fractions were prepared. A is a Coomassie-stained gel of concentrated supernatants. Molecular-mass markers (in kDa) are labeled on the left of A. B–E are immunoblots of gels identical to A probed with antisera against ExoU, ExoS/T, ExoY, and PopD, respectively. For ExoY expression in strain PA103, ExoY was amplified with its native promoter and cloned into pUCP18. ∗ denotes the expression of a catalytically (K81M) inactive form of ExoY.