Multiple displacement amplification

Multiple displacement amplification (MDA) is a non-PCR based DNA amplification technique. This method can rapidly amplify minute amounts of DNA samples to a reasonable quantity for genomic analysis. The reaction starts by annealing random hexamer primers to the template: DNA synthesis is carried out by a high fidelity enzyme, preferentially Φ29 DNA polymerase, at a constant temperature. Compared with conventional PCR amplification techniques, MDA generates larger sized products with a lower error frequency. This method has been actively used in whole genome amplification (WGA) and is a promising method for application to single cell genome sequencing and sequencing-based genetic studies.

Many biological and forensic cases involving genetic analysis require sequencing of DNA from minute amounts of sample, such as DNA from uncultured single cells or trace amounts of tissue collected from crime scenes. Conventional Polymerase Chain Reaction (PCR)-based DNA amplification methods require sequence-specific oligonucleotide primers and heat-stable (usually Taq) polymerase, and can be used to generate significant amounts of DNA from minute amounts of DNA. However, this is not sufficient for modern techniques which use sequencing-based DNA analysis. Therefore, a more efficient non-sequence-specific method to amplify minute amounts of DNA is necessary, especially in single cell genomic studies.

Bacteriophage Φ29 DNA polymerase is a high-processivity enzyme that can produce DNA amplicons greater than 70 kilobase pairs. Its high fidelity and 3’–5' proofreading activity reduces the amplification error rate to 1 in 10⁶−10⁷ bases compared to conventional Taq polymerase with a reported error rate of 1 in 9,000. The reaction can be carried out at a moderate isothermal condition of 30 °C and therefore does not require a thermocycler. It has been actively used in cell-free cloning, which is the enzymatic method of amplifying DNA in vitro without cell culturing and DNA extraction. The large fragment of Bst DNA polymerase is also used in MDA, but Ф29 is generally preferred due to its sufficient product yield and proofreading activity.

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