A Mutation in the 5′ Untranslated Region Increases Stability of norA mRNA, Encoding a Multidrug Resistance Transporter of Staphylococcus aureus

Abstract

NorA, a multidrug efflux pump in Staphylococcus aureus, protects the cell from multiple drugs, including quinolones. The flqB mutation (T3G) in the 5 untranslated region upstream of norA causes norA overexpression of 4.9-fold in cis, as measured in norA::blaZ fusions. The transcriptional initiation site of norA was unchanged in mutant and wild-type strains, but the half-life of norA mRNA was increased 4.8-fold in the flqB mutant compared to the wild-type strain. Computer-generated folding of the first 68 nucleotides of the norA transcript predicts an additional stem-loop and changes in a putative RNase III cleavage site in the flqB mutant.

Frequency and Genetic Characterization of Multidrug-Resistant Mutants of Staphylococcus aureus after Selection with Individual Antiseptics and Fluoroquinolones.

“…2). 13,14) The level of norA transcripts was markedly higher in the five norA mutants than that in the parent strain, RN2677 (Fig. 3).…”

“…In the mutant TP178, the site of norA mutation was identical to that in the MT23142 mutant with a flqB mutation and the SA1199B mutant. 3,13) Fournier et al suggested that the flqB mutation (T→G) confers an altered mRNA secondary structure that protects a putative cleavage site of RNase III and lead to increased norA mRNA stability. 13) However, the norA mutations in the TP178 (T→C) and SA-1199B (T→A) mutants differ from the flqB mutation.…”

“…3,13) Fournier et al suggested that the flqB mutation (T→G) confers an altered mRNA secondary structure that protects a putative cleavage site of RNase III and lead to increased norA mRNA stability. 13) However, the norA mutations in the TP178 (T→C) and SA-1199B (T→A) mutants differ from the flqB mutation. 4,5) Further studies are necessary to elucidate the mechanism of increased norA expression in the TP178 and SA1199B mutants.…”

“…1). Each mutation was located in the norA promoter, 13) with the exception of the mutation in TP178, which was located in the 5Ј untranslated region. To determine whether norA transcription might be altered by the various mutations, we examined the site of initiation of transcription and the level of norA transcripts in five norA mutants (TP171, TP172, TP176, TP180, TP185) (Figs.…”

The Role of the Transcription Factors MtrR and MtrA in the Fitness of the Pathogen Neisseria gonorrhoeae

“…The detection of high levels of mtrC transcript in this strain in the absence of changes in the expression of known regulators of the mtrCDE operon suggests there may be a difference in mtrC mRNA transcript stability. A similar mutation in the 5' untranslated region of an efflux pump gene was described for the NorB efflux pump of Staphylococcus aureus, which led to an increase in norB mRNA half-life (49). Therefore, we tested whether there was a difference in the mtrC mRNA half-life between mutant DW131 and the parent strain FAI9.…”