Atrans-acting leader RNA from aSalmonellavirulence gene

Abstract

Bacteria use flagella to move toward nutrients, find its host, or retract from toxic substances. Because bacterial flagellum is one of the ligands that activate the host innate immune system, its synthesis should be tightly regulated during host infection, which is largely unknown. Here, we report that a bacterial leader mRNA from themgtCBRvirulence operon in the intracellular pathogenSalmonella entericaserovar Typhimurium binds to thefljBcoding region of mRNAs in thefljBAoperon encoding the FljB phase 2 flagellin, a main component of bacterial flagella and the FljA repressor for the FliC phase 1 flagellin, and degradesfljBAmRNAs in an RNase E-dependent fashion during infection. A nucleotide substitution of thefljBflagellin gene that prevents themgtCleader RNA-mediated down-regulation increases thefljB-encoded flagellin synthesis, leading to a hypermotile phenotype inside macrophages. Moreover, thefljBnucleotide substitution rendersSalmonellahypervirulent, indicating that FljB-based motility must be compromised in the phagosomal compartment whereSalmonellaresides. This suggests that this pathogen promotes pathogenicity by producing a virulence protein and limits locomotion by atrans-acting leader RNA from the same virulence gene during infection.