SUBUNIT INTERACTIONS IN ABC TRANSPORTERS - A CONSERVED SEQUENCE IN HYDROPHOBIC MEMBRANE-PROTEINS OF PERIPLASMIC PERMEASES DEFINES AN IMPORTANT SITE OF INTERACTION WITH THE ATPASE SUBUNITS

The cytoplasmic membrane proteins of bacterial binding protein-depende nt transporters belong to the superfamily of ABC transporters, The hyd rophobic proteins display a conserved, at least 20 amino acid EAA---G- --------I-LP region exposed in the cytosol, the EAA region, We mutagen ized the EAA regions of MalF and MalG proteins of the Escherichia coli maltose transport system, Substitutions at the same positions ire Mal F and MalG have different phenotypes, indicating that EAA regions do n ot act symmetrically Mutations in malG or malF that slightly affect or do not affect transport, determine a completely defective phenotype w hen present together This suggests that EAA regions of MalF and MalG m ay interact during transport, Maltose-negative mutants fall into two c ategories with respect to the cellular localization of the MalK ATPase : in the first, MalK is membrane-bound, as in wild-type strains, while in the second, it is cytosolic, as in strains deleted in the malF and malG genes, From maltose-negative mutants of the two categories, we i solated suppressor mutations within malK that restore transport, They map mainly in the putative helical domain of MalK, suggesting that EAA regions may constitute a recognition site far the ABC ATPase helical domain.