Molecular characterization and expression of the dipeptide permease (Dpp) operon of Escherichia coli

Abstract

T he d ip ep tid e perm ease (Dpp) of Escherichia coli transports dipeptides consisting o f Lam ino acids. T he periplasm ic com ponent o f the D pp, the dipeptide-binding protein (D BP) encoded by the dppA gene, also serves as a chem oreceptor. I have sequenced the entire dpp lo cu s, w hich com prises an operon o f five genes, dppABCDE. Its genetic organization is the sam e a s that o f the oligopeptide perm ease (opp) operon o f Salmonella typhimurium and the spoOK o peron o f Bacillus subtilis. T he genes o f the dpp operon also are closely related to the gene encoding the H bpA hem e-binding lipoprotein and four genes com prising an unlinked operon o f unknow n function in Haemophilus influenzae. Each Dpp protein has its O pp, SpoOK and H. influenzae hom ologue. G row th o f hemA m utants at low external co n cen tratio n s o f the hem e precursor 5-am inolevulinic acid specifically requires D B P, and p o ly clo n al D B P antiserum cross-reacts w ell with H bpA . T ranscription o f the dpp operon in itia te s 165 b ases u p stream o f the p re d ic te d d pp A start codon. T he start site for transcription is preceded by potential -35 and -10 regions o f a prom oter. The deviation from the co n sen su s at the three least-conserved positions in the -10 region o f the predicted dpp p ro m o te r is ch aracteristic o f prom oters th at are u n d er the control o f transcriptional activators. D uring exponential grow th in LB broth the level of dpp m R N A increases in at least tw o steps, o ne betw een OD59Qn m 0.2 and 0 .4 and one between O D 5 9 o nm 0.7 and 1.0. T he 310 nucleotides betw een dppA and dppB include a R IP (repetitive IH F -b in d in g palindrom ic) elem ent. D eletion o f the R IP elem ent from a m ulti-copy plasm id causes 5 fold and 11 fold reductions in the levels o f upstream and dow nstream dpp m RNA.