sigma(54) Promoters control expression of genes encoding the hook and basal body complex in Rhodobacter sphaeroides

Gene expression of the flagellar system is tightly controlled by external s timuli or intracellular signals. A general picture of this regulation has b een obtained from studies of Salmonella enterica serovar Typhimurium. Howev er, these regulatory mechanisms do not apply to all bacterial groups. In th is study, we have investigated regulation of the flagellar genetic system i n Rhodobacter sphaeroides. Deletion analysis, site-directed mutagenesis, an d 5'-end mapping were conducted in order to identify the fliO promoter. Our results indicate that this promoter is recognized by the factor sigma(54). Additionally, 5'-end mapping of the flgB and fliK transcripts suggests tha t these mRNAs are also transcribed from sigma(54) promoters. Finally, we sh owed evidence that suggests that fliC transcription is not entirely depende nt on the presence of a complete basal body-hook structure. Our results are discussed in the contest of a possible regulatory hierarchy controlling fl agellar gene expression in R. sphaeroides.