An oligonucleotide-directed, in vitro mutagenesis method using ssDNA and preferential DNA amplification of the mutated strand.

The sequential addition of primers in a PCR enables one to preferentially amplify one of the two strands of a heteroduplex DNA template. This serves as the basis for a novel site-directed mutagenesis technique involving a heteroduplex DNA template that has been generated from a single-stranded, wild-type template and one or more mutagenic oligonucleotides. This preferential PCR method yields a mutation efficiency greater than 90% (consistent with the theoretical estimate for the method). The ability to generate multiple mutants also enables the screening of potential mutants by restriction endonuclease digestion.