Mutant loxP sites
From 2006.igem.org
If the CRE/LoxP mechanism for inversion we will need to create mutant loxP sites so that there will only be one inversion. The mutant lox P sites can be created using PCR and two pairs of partially overlapping primers.
see Plasmids under the Methods section http://nar.oxfordjournals.org/cgi/content/full/30/17/e90