Over 20 orthogonal serine integrases have been characterized to date (6,11), and many now have identified RDFs.

unique selling point of the latter systems is their one-way directional nature

attP and attB sites for serine integrases are both short (attP ∼50 bp; attB ∼40 bp); each site is bound by a dimer of integrase, and no host-encoded proteins are required

attB and attP sites are typically ≤ 50 bp with different inverted repeat sequences flanking 2 to 12 bp of complementary sequence, which includes the recombination crossover point