Pseudo-loxP genomic site (pseudo-loxP)

Pseudo-loxP genomic sites are naturally occurring DNA sequences in mammalian genomes that exhibit partial sequence identity to the 34-bp loxP site from bacteriophage P1 (Thyagarajan et al., 2000). These sites serve as unintended substrates for Cre recombinase, an enzyme widely used in genetic engineering to catalyze site-specific recombination. While Cre is highly specific, its activity at pseudo-loxP sites can lead to off-target genomic alterations, including large-scale deletions and chromosomal translocations, which may result in cellular toxicity or oncogenic transformations (Loonstra et al., 2001). In the context of therapeutic development, these sites are being explored as targets for evolved recombinases designed to recognize specific endogenous sequences for gene correction or viral excision. For example, the engineered Tre recombinase targets a pseudo-loxP site within the HIV-1 genome to excise the provirus from host cells (Sarkar et al., 2007). Consequently, pseudo-loxP sites represent both a significant safety hurdle for traditional Cre-lox systems and a potential opportunity for precision genome editing (Buchholz & Stewart, 2001). Understanding the distribution and accessibility of these sites is essential for improving the safety and precision of recombinase-based genomic medicines.

Other names

Cryptic loxP siteEndogenous loxP-like sequencePseudo-loxP sequence

Site-specific DNA recombination involving synapsis, cleavage, strand exchange, and ligation of DNA at sequences resembling the loxP site.