Recombinases classes

According to their catalytic amino acid, site specific recombinases are divided between two families: Tyrosine recombinases and serines recombinases.

These two classes are well separated and have probably arisen and evoluted separately.

They also differs greatly by their recombination mechanism: "Planar" Holliday Junction resolution for tyrosines recombinases vs Double strand breacks and rotation for serine recombinases.

=Tyrosine recombinases=

generalities

 * small sequence conservation
 * catalytic tyrosine in C-terminus
 * Holliday junction intermediate

Members and natural functions

 * Lambda Integrase: integration/excision of Lambda phage genome
 * Cre: excision: dimer reduction in phage P1 plasmid
 * FimB/FimE: inversion: alternate gene expression (e.coli fimbrial phase variation)
 * FLP: inversion amplification of yeast 2μm plasmid

Mechanism
Tetramere assembly, DNA inside, with half of the site reactivity: 2 monomers are actives at a time. Holliday junction isomerisation required.

=Serine Recombinases=
 * good sequence conservation
 * N-Ter catalytic serine
 * Double Strand Breaks and 180° rotation

Members and Natural functions

 * Hin: inversion (alternate gene expression Salmonella flagellar phase variation
 * Gin, Cin: inversion (alternate gene expresssion of tails fiber proteins in phages Mu and P1)
 * PhiC31: integration Streptomyces
 * bbx1: integration
 * TP901-1: integration/excision of lactococcaltemperate phage TP901-1 in Lactococcus lactis.
 * Tn3: resolvase: excision=resolution of cointegrates
 * γδ resolvase: idem

Mechanism
Tetramere assembly, DNA outside, 4 breaks (2 DSBs) at the same time,half of the complex 180° make a rotation