The activity of the two almost identical K M -uptake systems, Trk H and Trk G , from Escherichia coli K-12 depends completely and partially on the presence of the trkE gene, respectively. trkE maps inside the sapABCDF operon, which encodes an ATP-binding cassette (ABC) transporter of unknown function from the subgroup of peptide-uptake systems. This study was carried out to clarify the role of sapABCDF gene products in the ATP dependence of the E. coli Trk systems. For this purpose ∆sapABCDF ∆trkG and ∆sapABCDF ∆trkH strains of E. coli containing plasmids with sap genes from either E. coli or Vibrio alginolyticus were used. All five plasmid-encoded E. coli Sap proteins were made in E. coli mini-cells.