Motility of Helicobacter priori is coordinately regulated by the transcriptional activator FlgR, an NtrC homolog

σ54 is the subunit of bacterial RNA polymerase that transcribes from promoters with enhancer elements bound by enhancer-binding proteins. By computer searches of Helicobacter pylori genomic sequences, chromosomal gene disruption, and RNA analyses, we have identified σ54-recognized promoters that regulate transcription of flagellar basal body and hook genes, as well as the enhancer-binding protein FlgR (flagellum regulator), a transactivating protein of the NtrC family. We demonstrate that FlgR is required for bacterial motility and transcription of five promoters for seven basal body and hook genes. In addition, FlgR acts as a repressor of transcription of the σ28-regulated flaA flagellin gene promoter, while changes in DNA topology repress transcription of the σ54-regulated flaB flagellin gene promoter. Our data indicate that regulation of flagellar gene expression in H. priori shows similarities with that in enterobacteriaceae and Caulobacter.