The . Typhi gene contains multiple functional promoters.

The . Typhi gene, which codes for the LysR-type transcriptional regulator LeuO, contains five forward promoters named P3, P1, P2, P5 and P4, and two reverse promoters, P6 and P7. The activity of the forward promoters was revealed by primer extension using gene reporter fusions in an . Typhi mutant strain. Likewise, the activity of the reverse promoters was revealed in an background. Derepression of the transcription of the chromosomal gene was confirmed by RT-PCR in the mutant. The P1 transcriptional reporter fusion, which contained only the major P1 promoter, had a lower expression in a mutant strain, indicating that the steady-state levels of the (p)ppGpp alarmone positively regulate it. In contrast, the P3, P5P4, P6 and P7 transcriptional fusions were derepressed in the background, indicating that the alarmone has a negative effect on their expression. Thus, the search for genetic regulators and environmental cues that would differentially derepress gene expression by antagonizing the action of the H-NS and Lrp nucleoid-associated proteins, or that would fine-tune the expression of the various promoters, will further our understanding of the significance that multiple promoters have in the control of LeuO expression.