A mutation in the 5′ untranslated region increases stability of norA mRNA, encoding a multidrug resistance transporter of Staphylococcus aureus

NorA, a multidrug efflux pump in Staphylococcus aureus, protects the cell from multiple drugs, including quinolones, The flqB mutation (T-->G) 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 mas 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.