the newly synthesised strand. The exonuclease activity of the enzyme is, like its polymerisation activity, highly processive and can degrade single-stranded oligonucleotides without dissociation. Co-operation or a 'delicate competition' between these two functional domains is essential, so as to ensure accurate elongation at an optimal rate. The exonuclease activity of the enzyme does impede its polymerisation capacity; inactivation of the exonuclease activity by site-directed mutagenesis meant that a 350 fold lower dNTP concentration was required to achieve the same rates of primer elongation seen in the wild type enzyme. Whole genome amplification Φ29 polymerase enzyme is already used in multiple displacement amplification (MDA) procedures (including in a number of commercial kits) whereby fragments tens of kilobases in length can be produced from non-specific hexameric primers annealing at intervals along the genome. The enzyme has many desirable properties that make it appropriate for whole genome amplification (WGA) by this method. High processivity. Proofreading activity. It is believed to be 1 or 2 orders of magnitude less error prone than Taq polymerase. Generates large fragments, over 10kb. Produces more DNA than PCR-based methods, by about an order of magnitude. Requires minimal amount of template; 10 ng suffices. Novel replication mechanism; multiple-strand displacement amplification. Random primers (hexamers) can be used, no need to design specific primers/target specific regions. No need for thermal cycling. Good coverage and a reduced amplification bias when compared to PCR-based approaches. There is speculation that it is the least biased of the WGA methods in use. References Further reading DNA replication Podoviridae