Amplification of the tetracycline resistance determinant of pAMalpha1 in Enterococcus faecalis requires a site-specific recombination event involving relaxase.

The small multicopy plasmid pAMalpha1 (9.75 kb) encoding tetracycline resistance in Enterococcus faecalis is known to generate tandem repeats of a 4.1-kb segment carrying tet(L) when cells are grown extensively in the presence of tetracycline. Here we show that the initial (rate-limiting) step involves a site-specific recombination event involving plasmid-encoded relaxase activity acting at two recombination sequences (RS1 and RS2) that flank the tet determinant. We also present the complete nucleotide sequence of pAMalpha1.