Polymerase Chain Reaction: An Emerging Tool for Research in Pharmacology

Polymerase chain reaction (PCR) is a technique that can amplify a specific DNA segment in vitro using two site specific primers that hybridise to opposite DNA strands. The method produces large amounts of specific DNA from a complex DNA template in a single enzymatic reaction within a matter of hours. Reaction mixture contains a double helix DNA, two target specific primers, dNTPs, a DNA polymerase and a Mg2+ containing buffer. PCR is carried out in three distinct steps i.e. denaturation step, annealing step and extension step, which are repeated many times. The efficiency of PCR is measured in terms of its specificity, yield and fidelity. Most of the disease pathologies are associated with an altered gene expression leading to a resultant increase or decrease in the activity of cellular proteins. PCR can be employed to quantify alterations in cellular mRNA encoding for such proteins. These proteins may serve as novel target sites for therapeutic intervention. This modified form of PCR is termed as reverse transcriptase PCR (RT-PCR). In situ PCR, another modified form of PCR, not only permits the quantification of mRNA but also the exact localisation of mRNA changes in a particular cell type in a given tissue. PCR has also been employed to amplify a family of related genes using degenerate oligo nucleotide primers (DOP). This strategy is known as homology screening or DOP-PCR and has successfully expanded several gene families such as cyclins and cyclin-dependent kinases. Besides these application of PCR in pharmacology, it also serves as a useful diagnostic tool