The gcvB gene encodes a small untranslated RNA involved in expression of the dipeptide and oligopeptide transport systems in Escherichia coli.

The Escherichia coli gcvB gene encodes a small RNA transcript that is not translated in vivo. Transcription from the gcvB promoter is activated by the GcvA protein and repressed by the GcvR protein, the transcriptional regulators of the gcvTHP operon encoding the enzymes of the glycine cleavage system. A strain carrying a chromosomal deletion of gcvB exhibits normal regulation of gcvTHP expression and glycine cleavage enzyme activity. However, this mutant has high constitutive synthesis of OppA and DppA, the periplasmic-binding protein components of the two major peptide transport systems normally repressed in cells growing in rich medium. The altered regulation of oppA and dppA was also demonstrated using oppA-phoA and dppA-lacZ gene fusions. Although the mechanism(s) involving gcvB in the repression of these two genes is not known, oppA regulation appears to be at the translational level, whereas dppA regulation occurs at the mRNA level.