Genetic analysis of the replication region of the Lactobacillus plasmid vector pPSC22.

The sequence and genetic organization of the 1,600-bp replication region of the Lactobacillus vector pPSC22, a plasmid derived from a 7-kb cryptic plasmid of L. plantarum used for the cloning of heterologous genes in several lactobacilli, were determined. Sequence analysis revealed the presence of a plus origin of replication containing the two functional elements nic and bind, required for initiation of the leading strands typical of the rolling circle (RC)-replicating plasmids belonging to the pLS1 family. Two open reading frames (copA and repA) were located within the Lactobacillus portion of pPSC22. The repA gene product, a 234-amino acid protein, showed homologies with the Rep protein of the streptococcal plasmid pLS1 and contained the three conserved domains detected in most Rep proteins of RC-replicating plasmids and ss-coliphages. The genetic organization of the replication region of pPSC22 shared relevant homologies with the lactococcal plasmids pWVO1 and pFX2.