Two Chemosensory Operons of Rhodobacter sphaeroides Are Regulated Independently by Sigma 28 and Sigma 54

Abstract

ABSTRACT Rhodobacter sphaeroides has a complex chemosensory system, with several loci encoding multiple homologues of the components required for chemosensing in Escherichia coli. The operons che Op2 and che Op3 each encode complete pathways, and both are essential for chemosensing. The components of che Op2 are predominantly localized to the cell pole, whereas those encoded by che Op3 are predominantly targeted to a discrete cluster in the cytoplasm. Here we show that the expression of the two pathways is regulated independently. Overlapping promoters recognized by σ 28 and σ 70 RNAP holoenzyme transcribe che Op2, whereas che Op3 is regulated by one of the four σ 54 homologues, RpoN3. The different regulation of these operons may reflect the need for balancing responses to extra- and intracellular signals under different growth conditions.