Cre (Cyclization recombination enzyme) is a member of the large family of recombinases. Cre recognizes Lox site loxP, a 34 bp sequence motif from the PI bateriophage. If a DNA segment is flanked by two loxP sites in the same orientation, Cre neatly excises the segment (for later degradation) leaving a single remaining loxP site in the DNA molecule. The Cre/Lox system was first developed in the late 1980's to artificially manipulate gene expression and extensive reviews of the system exist (1).
