FIG 8.

Model for the differential posttranscriptional regulation of smeABR by peTrpL, antimicrobial compounds, and the antisense RNA as-smeR. Gene smeR encodes the repressor of the smeABR operon. Upon exposure to the SmeABR substrates Tc, Em, Cl, or Gs, transcription of the tricistronic smeABR mRNA and as-smeR RNA from promoters P_se (12) and P_as (this work), respectively, is induced. The peTrpL peptide, together with one of the mentioned antibiotics or the flavonoid, forms an ARNP complex with the as-smeR and smeR RNAs, which are then degraded. This leads to smeR downregulation and ensures upregulation of smeAB encoding the major MDR efflux pump of S. meliloti.