Ligase chain reaction

The ligase chain reaction (English ligase chain reaction, LCR) since 1989 is a method for detecting minute amounts of genetic material ( DNA). It functions similarly to the polymerase chain reaction, but using a different enzyme ( instead of the polymerase, a ligase ). Two samples per DNA strand can be ligated to a sample. The resulting, often only 30-50 bp amplicons of a cycle are used in the following cycles itself again as a starting point for the supplemented primer.

Since there is a polymerase activity within the LCR, the LCR is the product of two originally separate oligonucleotides which are covalently linked by the ligase.

The detection of the ligated LCR products achieved, for example, by measurement of ionizing radiation or by enzyme immunoassay (EIA) by labeling the 3'-and 5' - ends (e.g., fluorescein or biotin) with different ligands, such that only the ligated products are the further detection in the assay available.

The LCR has been used experimentally as a detection system for detecting bacterial and viral DNA, for example, the human papilloma virus ( Bond 1990, Hampl 1991) or Mycobacterium tuberculosis ( Barany, 1991) or for the detection of point mutations using allele-specific primers. The detection threshold for these systems was given as 200-1000 target molecules. Even in tumor diagnosis, the LCR is their application. The LCR provides compared to the Taq polymerase has the advantage that base mismatches (English mismatches ) can not be amplified, if not indeed caused by the enzyme activity, so that the LCR can be moved with very high cycle numbers from 50-70, without an increase of non-specific observed products. Therefore, the ligase chain reaction is also used for the detection of SNPs.