Recombinases classes

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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