Part of the ProU ABC transporter complex involved in glycine betaine and proline betaine uptake. Binds glycine betaine and proline betaine with high affinity. The complex is composed of two ATP-binding proteins (ProV), two transmembrane proteins (ProW) and a solute-binding protein (ProX). Induced in response to increased extracellular osmolarity, this is the third gene of the proU operon (proV-proW-proX). Osmoregulation requires curved DNA downstream of the transcription start site in proV, which is repressed when bound by H-NS. H-NS may act indirectly to influence the local topology of the promoter (PubMed:1423593).