Site‐specific Recombination in Chromosome Function

Abstract

Site‐specific recombination leads to the integration, deletion or inversion of defined DNA segments by conservative breakage–rejoining reactions at defined recombination sites. It functions to integrate and excise extrachromosomal elements into and out of genomes, to maintain circular replicons at the correct copy number in a monomeric state, and to mediate inversion gene switches.

Keywords: site‐specific recombination; resolvase; invertase; integrase

Figure 1.

(a)Schematic of the recombination core sites of a serine and tyrosine recombinase(not to scale). The 2‐bp and 6–8‐bp central (overlap) regions liebetween the sites of recombinase‐mediated cleavage (arrows). Recombinasemolecules are depicted as ovoids containing their respective nucleophiles. (b)Organization of the bacteriophage λ attP and attBrecombination sites. Recombinase‐binding sites are indicated by arrows (solidlines for core binding and dashed lines for binding to the accessory sequencearms P and P′; different regions of the recombinases contact thesedifferent types of site). Binding sites for the accessory proteins IHF, FIS and Xis are also indicated. Recombination between attP and attB generates attL (P′ plus core) and attR (P plus core).

Figure 2.

Outcomes of site‐specific recombination.

Figure 3.

Role ofaccessory sequences and proteins in resolution and inversion selectivity. (a)The recombination site for Tn3 and γδ resolvase containsa core site (site I) and two adjacent accessory sites (sites II and III). Allthree sites bind two molecules of resolvase. Recombination occurs at site I,and resolvase bound at sites II and III acts as an accessory protein thatentraps three plectonemic supercoils. Intramolecular recombination between twodirectly repeated (DR) sites forms a −2 catenane recombinant product.The specific geometry of the synapse restricts recombination to intramolecularevents between directly repeated molecules. (b) Schematic of synapsed directlyrepeated (DR) cer sites, the substrate for recombination by XerCD. Inthis case the accessory sequences (AS) are bound by ArgR and PepA. A −4catenane results from recombination. In reality, the recombination sites maysynapse in a close to antiparallel orientation, making an extra node entrappedbetween the recombination sites in addition to the three shown. (c) Schematicof synapsed inverted (IR) gix sites, the substrate for Gin invertase.Binding of the accessory protein, FIS to a distant enhancer site (E), entraps two negative supercoils, and thereby ensures inversion selectivity.

Figure 4.

(a)Reaction pathway for serine recombinases. (b) Reaction pathway for tyrosinerecombinases. (c) Chemistry of serine recombinase‐mediated site‐specificrecombination. (d) Chemistry of tyrosine recombinase‐mediated site‐specificrecombination.

Figure 5.

Threestrategies for Hin, Gin and Fim invertase‐mediated gene switches. Invertedrecombination sites are shown as horizontal arrows. Promoters and theirtranscripts are shown by p (promoter) followed by a zig‐zag line indicatingthe transcript.

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References

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Further Reading

Hallet B and Sherratt DJ (1997) Transposition and site‐specific recombination: adapting DNA cut‐and‐paste mechanisms to a variety of genetic rearrangements. FEMS Microbiology Reviews 21: 157–178.

Nash HA (1996) Site‐specific recombination: integration, excision, resolution, and inversion of defined DNA segments. In: Neidhart FE, Curtiss III R, Ingraham JL et al. (eds) Escherichia coli and Salmonella typhimurium. Cellular and Molecular Biology, pp. 2363–2376. Washington DC: ASM Press.

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How to Cite close
Sherratt, David J(Apr 2001) Site‐specific Recombination in Chromosome Function. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1038/npg.els.0001499]