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The antiterminator RfaH is required for the expression of LPS, capsule, haemolysin, exotoxin, haemin uptake receptor and F pilus. As these structures are critical for bacterial virulence, loss of RfaH usually leads to attenuation. Here, we inactivated the rfaH gene of Yersinia enterocolitica O:3 to study its role in this enteropathogen. RNA sequencing of the WT and ΔrfaH strain transcriptomes revealed that RfaH acted as a highly specific regulator that enhanced the transcription of the operons involved in biosynthesis of LPS O-antigen and outer core (OC), but did not affect the expression of enterobacterial common antigen. Interestingly, the transcriptome of the ΔrfaH strain was very similar to that of an O-antigen-negative mutant. This indicated that some of the changes seen in the ΔrfaH strain, such as the genes involved in outer membrane homeostasis or in the stress-response-associated Cpx pathway, were actually …