Cryptic loxP site

Cryptic loxP-like DNA sequences, often referred to as pseudo-loxP sites, are endogenous regions within mammalian genomes that share partial sequence homology with the 34-base pair loxP site from bacteriophage P1 [1]. While these sequences do not serve a known physiological function in humans, they become significant in the context of biotechnology and gene therapy when Cre recombinase is introduced into cells [2]. Cre recombinase, an enzyme used to catalyze site-specific recombination between loxP sites, can mistakenly recognize these cryptic sequences as legitimate targets [3]. This off-target recognition leads to unintended DNA strand exchange, resulting in genomic rearrangements such as deletions, inversions, and chromosomal translocations [1][4]. Such events can cause significant cellular stress, manifesting as “Cre-induced toxicity,” which includes DNA damage responses, cell cycle arrest, and apoptosis [2]. Consequently, these sequences represent a major safety concern for the development of Cre-based therapeutic interventions and require careful genomic screening or the engineering of high-fidelity recombinases to minimize adverse effects [3].

Other names

Pseudo-loxP siteloxP-like sequenceEndogenous loxP-like elementNon-specific and cryptic loxP-like DNA sequences in the genome

Cre recombinase recognizes and binds to these endogenous sequences that mimic the 34-bp loxP recognition site, catalyzing unintended DNA recombination, which can lead to deletions, inversions, or translocations [1][2].