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

recombination site structure

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