Part of the ProU ABC transporter complex involved in glycine betaine and proline betaine uptake. Probably responsible for the translocation of the substrate across the membrane. 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 second 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). Belongs to the binding-protein-dependent transport system permease family. CysTW subfamily.