Part of the plasmid amplification system, which corrects any decrease in copy number caused by a rare missegregation event. Catalyzes the recombination between the large inverted repetitions of the 2-micron plasmid during plasmid replication. This recombination event changes the direction of one of the two replication forks in the bidirectionally replicating molecule, effectively resulting in multiple rounds of replication from a single initiation event. Binds specifically to the FLP recognition target (FRT) site where it induces DNA to bend. Three types of bend exist. Type I is approximately 60 degrees and results from 1 FLP molecule binding to 1 symmetry element. Type II is >144 degrees and results from FLP molecules binding to symmetry elements a and b. Type III is approximately 65 degrees and results from FLP molecules binding to symmetry elements b and c. Homotetramer. Repressed by the negative regulatory complex REP1-REP2. The plasmid 2-micron circle is a extrachromosomal element that resides in the nucleus and propagates itself stably in host cell populations. It provides no obvious advantage to the host but imposes no significant disadvantage either at its steady-state copy number of 40-60 molecules/cell. Belongs to the 'phage' integrase family.