Integrase
Also known as: site-specific integrase, phage integrase
A serine or tyrosine recombinase derived from bacteriophages that catalyzes unidirectional DNA integration between specific attachment sites, enabling stable genomic insertion.
Integrase is a recombinase enzyme, typically derived from temperate bacteriophages, that mediates the insertion of phage DNA into a host chromosome by catalyzing recombination between phage attachment site (attP) and bacterial attachment site (attB) 1.
How It Works
Serine integrases such as Bxb1, phiC31, and TP901-1 catalyze recombination between non-identical attB and attP sites to produce hybrid attL and attR sites. Crucially, the integrase alone cannot reverse this reaction — reversal requires both the integrase and an accessory recombination directionality factor (RDF). This unidirectionality makes serine integrases ideal for building irreversible genetic switches and stable genomic insertions.
For genomic integration, a landing pad containing an attB site is first installed in the host chromosome. The gene of interest, flanked by an attP site on the delivery vector, is then integrated at this defined locus through integrase-mediated recombination. This approach provides single-copy, position-defined insertion — avoiding the copy number variation and potential insertional mutagenesis of random integration methods.
In genetic circuit design, integrases serve as biological memory elements. A pulse of integrase expression permanently flips a DNA segment between two attachment sites, toggling a reporter or functional gene between on and off states. This state persists indefinitely through cell division. Libraries of orthogonal integrases that do not cross-react with each other’s attachment sites enable multi-bit memory devices.
Computational Considerations
Genomic mining pipelines identify novel integrases and their cognate attachment sites from sequenced phage genomes, expanding the available orthogonal toolkit 2. Computational models predict cross-reactivity between integrase-attachment site pairs, enabling selection of non-interfering combinations for complex circuit architectures with multiple independent memory registers.
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Bioinformatic mining of phage genomes has identified large libraries of orthogonal integrases, and computational models predict attachment site specificity to expand the toolkit for genetic memory circuits.