Figure 2

Effect of various deletions in sseB on synthesis and secretion of SseB in vitro. S. Typhimurium WT or ΔsseB without plasmid, harboring plasmid psseB for complementation of the sseB deletion, or plasmids for the expression of various sseB mutant alleles (psseB Δx) were grown in 400 ml minimal medium PCN-P (0.4 mM) at pH 5.8 to induce SPI2 expression as well as protein secretion by the SPI2-T3SS. For analyses of protein synthesis, equal amounts of bacterial cells as adjusted by OD₆₀₀ were harvested and resuspended in SDS-PAGE sample buffer (T, total cell fraction). Secreted protein bound to the bacterial surface was released by mechanical shearing and precipitated from bacteria-free supernatant (D, detached fraction) and secreted proteins in the supernatant were precipitated by addition of 10% TCA (final concentration). For Western blot analysis, samples corresponding to equal amount of bacteria or supernatant were separated by SDS-PAGE and transferred to nitrocellulose membranes and protein was detected with antiserum raised against SseB. As loading control and control for cell lysis, the bacterial heat shock protein DnaK was detected. The position of SseB and various mutant forms of SseB was indicated by asterisks. The quantification of the signal intensities is shown in Additional file 1.