Expression of the class 2 genes in the spiC mutant. (A) β-galactosidase activity from fliA-lacZ transcription fusion expressed by wild-type Salmonella (WT) and spiC mutant strain grown in LB to an OD600 of 1.6. β-galactosidase activity is expressed in Miller units. WT (pRL124) carries the vector with the promoterless lacZ. Quantitative analysis of fliA (B), flgB (C), or fliF (D) mRNA expression. Bacteria were cultured in LB, and the total RNA was extracted from the wild-type Salmonella, spiC mutant strain, or spiC mutant strain carrying pEG9127 (spiC+) when the OD600 was 1.6. Quantitative RT-PCR was conducted using a TaqMan probe. Levels of each mRNA were normalized to the 16S rRNA concentration, and the results are shown relative to the expression in the wild-type strain. The expression levels of the fliA, flgB, or fliF gene in the spiC mutant were greatly reduced compared to the wild-type strain.