THE DIPEPTIDE PERMEASE OF ESCHERICHIA-COLI CLOSELY RESEMBLES OTHER BACTERIAL TRANSPORT-SYSTEMS AND SHOWS GROWTH-PHASE-DEPENDENT EXPRESSION

The dipeptide permease (Dpp) of Escherichia coli transports peptides consisting of two or three L-amino acids, The periplasmic dipeptide-binding protein (DBP), encoded by the dppA gene, also serves as a chemoreceptor. We sequenced the dpp locus, which comprises an operon of five genes, dppABCDE. Its organization is the same as the oligopeptide permease (opp) operon of Salmonella typhimurium and the spoOK operon of Bacillus subtilis. The dpp genes are also closely related to the hbpA gene, which encodes a haem-binding lipoprotein, and four other genes in an unlinked operon of unknown function in Haemophilus influenzae. Each Dpp protein has an Opp, SpoOK and H, influenzae homologue. Transcription of the dpp operon initiates 165 bases upstream of the predicted dppA start codon. The start site for transcription is preceded by potential -35 and -10 regions of a sigma(70) promoter. During exponential growth in Luria-Bertani (LB) broth, the level of dpp mRNA increases in two steps, one between A(590) 0.2 and 0.4 and one between A(590) 0.7 and 1.0. The 310 nucleotides between dppA and dppB include a RIP (repetitive IHF-binding palindromic) element, whose deletion from a multi-copy plasmid causes fivefold and 10-fold reductions in the levels of upstream and downstream dpp mRNA, respectively.