Creative Biogene’s Easy-Change® XL Site-Directed Mutagenesis Kit allows site specific mutation in virtually any double-stranded plasmid, thus eliminating the need for subcloning into M13-based bacteriophage vectors and for ssDNA rescue. In addition, the Easy-Change® XL system requires no specialized vectors, unique restriction sites, or multiple transformations. This rapid four-step procedure generates mutants with greater than 80% efficiency. The protocol is simple and uses either miniprep plasmid DNA or cesium-chloride-purified DNA.