Flippase optimized (Flpo)
Mouse codon-optimized FLP recombinase achieving Cre-like recombination efficiency through extensive sequence optimization. Engineered via GeneOptimizer algorithm with modified codon usage, removal of cryptic splice sites and TATA boxes, and altered G/C content for enhanced mRNA stability. Includes SV40 nuclear localization signal for efficient nuclear targeting.
Origin: Engineered from Saccharomyces cerevisiae FLP via mouse codon optimization
Characteristics
Recombination efficiency comparable to Cre recombinase, representing >20-fold improvement over FLPe variant. Mouse codon usage optimization increases steady-state protein expression in mammalian cells. Modified base composition with optimized G/C content prolongs mRNA half-life compared to native yeast-derived sequence. Incorporates dual stop codons for efficient translational termination and C-terminal SV40 NLS for nuclear localization. Recognizes 34 bp FRT sites with bidirectional recombination activity. Widely distributed via Addgene plasmid repository for academic research applications.
Applications: Conditional gene activation and inactivation in mammalian cell lines and transgenic mice. Enables dual-recombinase genetic strategies when combined with Cre-loxP system for complex genomic manipulations requiring orthogonal site-specific recombination. Widely adopted in neuroscience research for cell-type-specific labeling and optogenetic applications. Facilitates FRT-mediated cassette exchange and marker excision in ES cells and primary cell cultures. Used in iPSC generation workflows and transgene removal applications requiring traceless excision.
Limitations: Requires pre-existing FRT target sites for recombination activity, limiting genomic targeting flexibility compared to programmable nucleases. Less extensive toolkit of reporter lines and conditional alleles compared to mature Cre-loxP system despite improved efficiency. FRT sites may undergo spontaneous recombination in presence of constitutive Flpo expression in some contexts.