Part of the binding-protein-dependent transport system for lactose. Probably responsible for the translocation of the substrate across the membrane. By lactose and various galactosides, and subject to catabolite repression by glucose, galactose and succinate. In strain AR50 the expression of the lac operon is constitutive. Belongs to the binding-protein-dependent transport system permease family. MalFG subfamily. It is uncertain whether Met-1 or Met-2 is the initiator.