The role of the small regulatory RNA GcvB in GcvB/mRNA posttranscriptional regulation of oppA and dppA in Escherichia coli

The gcvB gene encodes two small, nontranslated RNAs that regulate OppA and DppA, periplasmic binding proteins for the oligopeptide and dipeptide transport systems. Analysis of the gcvB sequence identified a region of complementarity near the ribosome-binding sites of dppA and oppA mRNAs. Several changes in gcvB predicted to reduce complementarity of GcvB with dppA-lacZ and oppA-phoA reduced the ability of GcvB to repress the target RNAs while other changes had no effect or resulted in stronger repression of the target mRNAs. Mutations in dppA-lacZ and oppA-phoA that restored complementarity to GcvB restored the ability of GcvB to repress dppA-lacZ but not oppA-phoA. Additionally, a change that reduced complementarity of GcvB to dppA-lacZ reduced GcvB repression of dppA-lacZ with no effect on oppA-phoA. The results suggest that different regions of GcvB have different roles in regulating dppA and oppA mRNA, and although pairing between GcvB and dppA mRNA is likely part of the regulatory mechanism, the results do not support a simple base pairing interaction between GcvB and its target mRNAs as the complete mechanism of repression.