Fig 1.
LcrF complements an exsA mutant for T3SS gene expression. (A to C) The PA103 exsA::Ω strain carrying either the PexoT-lacZ (A), PexsC-lacZ (B), or PexsD-lacZ (C) transcriptional reporter was transformed with a vector control (pJN105), an ExsA expression vector (pExsA), or an LcrF expression vector (pLcrF). The resulting strains were cultured under noninducing (−EGTA, open bars) or inducing (+EGTA, hatched bars) conditions for T3SS gene expression and assayed for β-galactosidase activity as reported in Miller units. *, P < 0.001; ** P < 0.01. (D) Silver-stained gel of concentrated culture supernatant fluid prepared from wild-type PA103 or the PA103 exsA::Ω strain carrying the indicated plasmids following growth under noninducing (−EGTA) or inducing (+EGTA) conditions for T3SS gene expression. The positions of molecular mass standards are indicated on the left side of the gel, and the type III secreted proteins ExoU, ExoT, PopB, PopD, PopN, and PcrV are labeled on the right side of the gel (49).