The 5.1-kb plasmid pAMα1Δ2, a derivative of the 9.6-kb plasmid pAMα1 which is harbored by Enterococcus faecalis ATCC 14508, has a region necessary for replication in E. faecalis. The nucleotide sequence related to the replication region in pAMα1Δ2 was determined and found to contain an open reading frame of 720-bp encoding a replication protein. The sequence showed 54.5 and 48.5% homology to those encoding the RepAs of plasmids pLA103 from Lactobacillus acidophilus and pFA3 from Neisseria gonorrhoeae, respectively. A recombinant 5.8-kb plasmid, pEFX6, which can be used as a shuttle vector between Escherichia coli and some strains of E. faecalis, was constructed by combining the tetracycline resistance gene of pAMα1Δ2 and the replication regions of pAMα1Δ2 and pUC18 for E. faecalis and E. coli, respectively. This shuttle vector was successfully used to clone and express the gelatinase gene from E. faecalis subsp. zymogenes IFO 3989 in E. faecalis C57, a strain showing no gelatinase activity.