The expression of the rpoE operon is fine-tuned by the internal rseAp promoter in Salmonella enterica serovar Typhimurium

Three promoters, located upstream of the rpoE gene encoding an extracytoplasmic sigma factor sigma (E), direct expression of the rpoE operon (rpoE, rseA, rseB, rseC) in Salmonella enterica serovar Typhimurium (S. Typhimurium). One of them, rpoEp3, has been found to be directly recognized by RNA polymerase containing sigma factor sigma (E). Using the Northern blot analysis we detected a complex pattern of transcripts indicating an internal promoter in the coding region of the rpoE gene. The promoter, rseAp, has been located by S1 mapping analysis. Its proposed -10 and -35 elements with 15 intervening nucleotides exhibited high similarity with the consensus sequence of sigma (E) promoters, suggesting the direct dependence of rseAp upon sigma (E). Activity of rseAp increased towards stationary phase, after heat shock, cold shock, and in the presence of artificially induced rpoE expression, the conditions previously shown to activate sigma (E)-dependent promoters. In vivo experiments revealed increase of the rseAp activity during growth and confirmed its clear dependence upon sigma (E). The proposed role of the internal rseAp promoter is to facilitate a feedback control of sigma (E) level after the envelope stress is removed.