Quantitative polymerase chain reaction with oligodeoxynucleotide ligation assay/enzyme-linked immunosorbent assay...

Quantitation of nucleic acids by the polymerase chain reaction (PCR) requires coamplification of a control nucleic acid, usually a variant of the sequence to be analyzed, which is added to the sample DNA and amplified in competition. Following PCR, amplified sample and control DNAs are separated by electrophoresis and quantitated, for example by measuring the radioactivity incorporated into the products during the PCR. The need for both electrophoretic separation and radioactive labeling has considerably impeded the use of PCR for routine purposes, e.g., in the clinical laboratory, which requires automatic processing of many samples in parallel. We describe here a quantitative PCR procedure which circumvents electrophoretic separation and detection by radioactivity. It uses a point mutated version of the sample DNA as an internal control. After competitive PCR, amplified sample and control DNA are distinguished by an oligodeoxynucleotide ligation assay (OLA) (Landegren et al., Science 241, 1077-1080, 1988) using two oligodeoxynucleotides, one carrying a biotin-group at the 5'-end and another one with either a digoxigenin (specific for sample DNA) or fluorescein moiety (specific for control DNA), respectively, incorporated close to the 3'-end. Biotinylated oligodeoxynucleotides, educts as well as products of the ligation reaction, are immobilized on avidin-coated microtiter plates. Quantitation of digoxigenin and fluorescein-labeled oligodeoxynucleotide ligation products is achieved by an enzyme-linked immunosorbent assay. This method is very well suited for fast automated or semiautomated PCR.