Practice question

Cre is a 38 kDa tyrosine recombinase encoded by bacteriophage P1 that catalyzes site-specific recombination without cofactors. Its target is loxP, a 34 base pair sequence containing an asymmetric 8 base pair core spacer flanked by two 13 base pair inverted repeats where Cre binds as dimer. Recombination between two loxP sites excises or inverts intervening DNA depending on orientation. Specificity for loxP distinguishes Cre from Flp which recognizes FRT, making Cre-loxP a powerful conditional genome manipulation tool in mammals.