DUPLICATION OF THE PEPF GENE AND SHUFFLING OF DNA FRAGMENTS ON THE LACTOSE PLASMID OF LACTOCOCCUS-LACTIS

The gene corresponding to the lactococcal oligopeptidase PepF1 (former ly PepF [V. Monnet, M. Nardi, A. Chopin, M.-C. Chopin, and J.-C. Gripo n, J. Biol. Chem. 269:32070-32076, 1994]) is located on the lactosepro teinase plasmid of Lactococcus lactis subsp. cremoris NCDO763. Use of the pepF1 gene as a probe with different strains showed that pepF1 is present on the chromosome of Lactococcus lactis subsp. lactis IL403, w hereas there is a second, homologous gene, pepF2, on the chromosome of strain NCDO763. From hybridization, PCR amplification, and sequencing experiments, we deduced that (i) pepF1 and pepF2 exhibit 80% identity and encode two proteins which are 84% identical and (ii) pepF2 is inc luded in an operon composed of three open reading frames and is transc ribed from two promoters, The protein, encoded by the gene located dow nstream of pepF2, shows significant homology with methyltransferases. Analysis of the sequences flanking pepF1 and pepF2 indicates that only a part of the pepF1 operon is present on the plasmid of strain NCDO76 3, while the operon is intact on the chromosome of strain IL1403. Trac es of several recombination events are visible on the lactose-proteina se plasmid. This suggests that the duplication of pepF occurred by rec ombination from the chromosome of an L. lactis subsp. lactis strain fo llowed by gene transfer. We discuss the possible functions of PepF and the role of its amplification.