Role of the sRNA GcvB in regulation of cycA in Escherichia coli

In Escherichia coli, the gcvB gene encodes a small non-translated RNA that regulates several genes involved in transport of amino acids and peptides (including sstT, oppA and dppA). Microarray analysis identified cycA as an additional regulatory target of GcvB. The cycA gene encodes a permease for the transport of glycine, D-alanine, D-serine and D-cycloserine. RT-PCR confirmed that GcvB and the Hfq protein negatively regulate cycA mRNA in cells grown in Luria-Bertani broth. In addition, deletion of the gcvB gene resulted in increased sensitivity to D-cycloserine, consistent with increased expression of cycA. A cycA: : lacZ translational fusion confirmed that GcvB negatively regulates cycA expression in Luria-Bertani broth and that Hfq is required for the GcvB effect. GcvB had no effect on cycA: : lacZ expression in glucose minimal medium supplemented with glycine. However, Hfq still negatively regulated the fusion in the absence of GcvB. A set of transcriptional fusions of cycA to lacZ identified a sequence in cycA necessary for regulation by GcvB. Analysis of GcvB identified a region complementary to this region of cycA mRNA. However, mutations predicted to disrupt base-pairing between cycA mRNA and GcvB did not alter expression of cycA:: lacZ. A model for GcvB function in cell physiology is discussed.