CLONING AND FUNCTIONAL EXPRESSION IN ESCHERICHIA-COLI OF THE GENE ENCODING THE DIPEPTIDE AND TRIPEPTIDE TRANSPORT PROTEIN OF LACTOBACILLUS-HELVETICUS

The gene encoding the di- and tripeptide transport protein (DtpT) of L actobacillus helveticus (DtpT(LH)) was cloned with the aid of the inve rse PCR technique and used to complement the dipeptide transport-defic ient and proline-auxotrophic Escherichia coil E1772. Functional expres sion of the peptide transporter,vas shown by the uptake of prolyl- [C- 14] alanine in whole cells and membrane vesicles, Peptide transport vi a DtpT in membrane vesicles is driven by the proton motive force. The system has specificity for di- and tripeptides but not for amino acids or tetrapeptides, The dtpT(LH) gene consists of 1,491 bp, which trans lates into a 497-amino-acid polypeptide. DtpT(LH) shows 34% identity t o the di- and tripeptide transport protein of Lactococcus lactis and i s also homologous to various peptide transporters of eukaryotic origin , but the similarity between these proteins is confined mainly to the N-terminal halves.