Simultaneous mutagenesis of multiple sites: application of the ligase chain reaction using PCR products instead of oligonucleotides.

A method is described for preparing mutants with multiple, site-directed mutations by ordered coupling of PCR-generated fragments catalyzed by a thermostable DNA ligase. Annealing of the sense strands of the fragments to a single-stranded (antisense) template created a full-length sense strand leaving only nicks that were closed by ligation. Mutations were introduced in the PCR primers. Following 40 cycles of denaturation and annealing, tags on the flanking primers of the ligase chain reaction product were used specifically to amplify the mutated product with specific primers that could not amplify the original template. The amplified ligation product was cloned and was found to contain the desired restriction sites introduced by way of the mutagenic primers.