Table I.

Site-specific DNA recombination systems used for genome engineering in mammalian cells.

Recombinase	Origin	Classification	Target site	Target sequence
Flp	S. cerevisiae	Tyrosine	FRT	5′-GAAGTTCCTATTCTCTAGAAAGTATAGGAACTTC-3′
KD	K. drosophilarum	Tyrosine	KDRT	5′-AAACGATATCAGACATTTGTCTGATAATGCTTCATTATCAGACAAATGTCTGATATCGTTT-3′
B2	Z. bailii	Tyrosine	B2RT	5′-GAGTTTCATTAAGGAATAACTAATTCCCTAATGAAACTC-3′
B3	Z. bisporus	Tyrosine	B3RT	5′-GGTTGCTTAAGAATAAGTAATTCTTAAGCAACC-3′
R	Z. rouxii	Tyrosine	RSRT	5′-TTGATGAAAGAATAACGTATTCTTTCATCAA-3′
Cre	Phage P1	Tyrosine	loxP	5′-ATAACTTCGTATAGCATACATTATACGAAGTTAT-3′
VCre	Vibriosp.	Tyrosine	VloxP	5′-TCAATTTCTGAGAACTGTCATTCTCGGAAATTGA-3′
SCre	Shewanellasp.	Tyrosine	SloxP	5′-CTCGTGTCCGATAACTGTAATTATCGGACATGAT-3′
Vika	V. coralliilyticus	Tyrosine	vox	5′-AATAGGTCTGAGAACGCCCATTCTCAGACGTATT-3′
Dre	Bacteriophage D6	Tyrosine	rox	5′-TAACTTTAAATAATGCCAATTATTTAAAGTTA-3′
λ-Int	Phage λ	Tyrosine	attP	5′-CAGCTTTTTTATACTAAGTTG-3′
			attB	5′-CTGCTTTTTTATACTAACTTG-3′
HK022	Phage HK022	Tyrosine	attP	5′-ATCCTTTAGGTGAATAAGTTG-3′
			attB	5′-GCACTTTAGGTGAAAAAGGTT-3′
φC31	Phage φC31	Serine	attP	5′-CCCCAACTGGGGTAACCTTTGAGTTCTCTCAGTTGGGG-3′
			attB	5′-GTGCCAGGGCGTGCCCTTGGGCTCCCCGGGCGCG-3′
Bxb1	Phage Bxb1	Serine	attP	5′-GGTTTGTCTGGTCAACCACCGCGGTCTCAGTGGTGTACGGTACAAACC-3′
			attB	5′-GGCTTGTCGACGACGGCGGTCTCCGTCGTCAGGATCAT-3′
Gin	Phage Mu	Serine	gix	5′-TTATCCAAAACCTCGGTTTACAGGAA-3′
Tn3	E. coli	Serine	res site I	5′-CGTTCGAAATATTATAAATTATCAGACA-3′

For the prototypical site-specific recombinases Cre, Flp, λ-Int, φC31, Gin and Tn3, crossover regions are underlined.