Targeted amplification of mutant strands for efficient site-directed mutagenesis and mutant screening

Site-directed mutagenesis is an invaluable tool for functional studies and genetic engineering. However, most current protocols require the target DNA to be cloned into a plasmid vector before mutagenesis can be performed, and none of them are effective for multiple-site mutagenesis. We now describe a method that allows mutagenesis on any DNA template (e.g. cDNA, genomic DNA, and plasmid DNA), and is highly efficient for multiple-site mutagenesis (up to 100%). The technology takes advantage of the requirement that, in order for DNA polymerases to elongate, it is crucial that the 3"² sequences of the primers match the template perfectly. When two outer mutagenic oligonucleotides (oligos) are incorporated together with the desired mutagenic oligos into the newly synthesized mutant strand, they serve as anchors for PCR primers which have 3"² sequences matching the mutated nucleotides, thus amplifying the mutant strand only. The same principle can also be used for mutant screening.