What is ligase chain reaction?

The ligase chain reaction (LCR) is a method of DNA amplification that involves a thermostable ligase to join two probes together which can then be amplified by standard polymerase chain reaction (PCR) cycling. Apart from the thermostable polymerase as needed in conventional PCR, LCR also requires another completely different enzyme, ligase, to work properly. The ligase is used to join the probe molecules together, which can then by amplified by the polymerase such as Taq polymerase.

While PCR is usually used to amplify a segment of DNA, LCR is used for the amplification of a short DNA probe that is involved in the ligation. In a typical LCR experiment, two probes are used, which are designed such that the 5’ end of one probe is directly adjacent to the 3’ end of the other probe, providing the reaction site for the ligase. If a mismatch is introduced in the probe (e.g. 3’ end) that can prevent the DNA ligation, LCR can also be used for the detection of single base mutation, where discriminated amplification can be observed between the normal and mutant DNA.