Hic2^{Gt(E225A08)Wrst}

The gene trap cassette is flanked by 2 pairs of variant LoxP sites (LoxP and Lox511) and 2 pairs of variant flippase recognition target sites (FRT and F3). The variant sites are designed to allow irreversible rotation of the genetrap cassette. Recombination between 2 variant sites in reverse orientation rotates the genetrap but leaves the other 2 variant sites in the same orientation on 1 side of the genetrap resulting in an excision event removing the possibility of a second rotation with the same enzyme. The genetrap can be recombined in this way twice, once with flippase (FLP) and once with CRE. This unrecombined allele expresses beta-galactosidase in place of exons 2 and 3. (J:225226)