Genetic analysis of Escherichia coli oligopeptide transport mutants

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Abstract
The composition of the outer membrane channels formed by the OmpE and OmpC porins is important in peptide permeation, and elimination of these proteins from the E. coli outer membrane results in a cell in which the primary means for peptide permeation through this cell structure has been lost. E. coli peptide transport mutants which harbor defects in genes other than the ompF/ompC genes were isolated on the basis of their resistance to toxic tripeptides. The genetic defects carried by these oligopeptide permease-negative (Opp-) strains were found to map in 2 distinct chromosomal locations. One opp locus was trp linked and mapped to the interval between att.vphi.80 and galU. Complementation studies with F''123 opp derivatives indicated that this peptide transport locus resembles that characterized in Salmonella typhimurium as a tetracistronic operon. The second opp locus, which is designated oppE, was mapped to the interval between dnaC and hsd at 98.5 min on the E. coli chromosome. The differences in peptide utilization, sensitivity and resistance to toxic peptides and the L-[U-14C]alanyl-L-alanyl-L-alanine transport properties observed with these Opp- E. coli strains demonstrated that the transport systems encoded by the trp-linked opp genes and by the oppE gene(s) have different substrate preferences. Mutants harboring defects in both peptide transport loci defined in this study would not grow on nutritional peptides except for tri-L-methionine. The mutants also were totally resistant to toxic peptides and would not actively transport L-[U-14C]alanyl-L-alanyl-L-alanine.