The term strand displacement describes the ability to displace downstream DNA encountered during synthesis. NEB produces DNA polymerases with varying degrees of strand displacement activity. T4 (NEB#M0203) and T7 (NEB #M0274) DNA Polymerases lack strand displacement activity, while phi29 (NEB #M0269) has a very strong ability to strand displace. These polymerases are active at moderate temperatures, around 20–37°C. Bst DNA Polymerase, Large Fragment (NEB #M0275) on the other hand is a good strand displacing enzyme that is active at elevated temperatures, around 65°C. Polymerases lacking strand displacement activity are used in gap-filling reactions, such as those in site-directed mutagenesis protocols. Protocols such as the isothermal amplification method termed Strand Displacement Amplification (SDA) exploit the ability to strand displace.
In contrast to strand displacement, some polymerases, such as Taq DNA polymerase (NEB #M0267), degrade an encountered downstream strand via a 5´→3´ exonuclease activity. This activity can be utilized for nick translation protocols.