| Cre recombinase is a bacteriophage P1–derived tyrosine type recombinase that catalyzes precise, site specific recombination between two 34 base pair loxP recognition elements, making it a cornerstone of modern genetic engineering and conditional gene control systems. The enzyme binds the symmetric inverted repeats flanking the asymmetric spacer region of each loxP site and induces sharp DNA bending, assembling a tetrameric synaptic complex in which two Cre dimers align two loxP sites to position the scissile phosphodiester bonds for coordinated cleavage and strand exchange. Within the active site, a conserved tyrosine residue acts as a nucleophile, forming a 3′ phosphotyrosine covalent intermediate with the DNA backbone, while the 5′ hydroxyl ends attack the corresponding phosphotyrosine complex on the partner strand, generating a Holliday junction like intermediate that is resolved to produce recombinant DNA with a defined outcome, deletion, inversion, or translocation, depending on the orientation and topology of the loxP sites. Cre loxP systems are used to generate tissue specific knockouts, inducible alleles, and lineage tracing models, with Cre expression driven by cell type specific promoters or tamoxifen regulated fusion constructs that link developmental, metabolic, and immune signaling pathways to targeted genetic perturbation in defined cell populations. Although naturally evolved to maintain the P1 phage–plasmid copy number, this tight, accessory factor independent mechanism has been adapted as a reliable, genome editable switch in mammalian cells, and its extensive structural and biophysical characterization underpins the rational design of improved variants and orthogonal recombinase systems. |
Lane 1: 293T (mock-transfected), Lane 2: 293T (transfected with Cre recombinase)
