Type III secretion system-encoding gene expression in Shigella sonnei. (A) Immunoblot analysis of IpaB and InvE at 30 °C (lanes 1–4) and 37 °C (lanes 5–8). Lanes: 1 and 5, MS390 (WT); 2 and 6, MS4831 (Δhfq); 3 and 7, MS5201 (ΔrodZ); lane 4, MS5201 carrying pBAD-rodZ; lane 8, MS5201 carrying pTrc-rodZ. (B) β-galactosidase activity of an invETx–lacZ transcriptional fusion reporter protein (pJM4320). (C) β-galactosidase activity of an invETL–lacZ translational fusion reporter protein (pJM4321). (B,C) Bars: 1, MS506 (NC, avirulent S. sonnei); 2, MS390 (WT S. sonnei); 3, MS390 at 37 °C; 4, MS5201 (ΔrodZ); 5, MS5201 (ΔrodZ) MS5201 carrying pBAD-rodZ; 6, MS5201 carrying pBAD18Kan. Error bars represent s.d. of four independent experiments. MU, Miller units; NC, negative control; WT, wild type.