Taq

Taq DNA polymerase, commonly referred to as Taq, is a thermostable enzyme used to synthesize DNA in the polymerase chain reaction (PCR). It is derived from the thermophilic bacterium Thermus aquaticus, which was found in hot springs. The enzyme reproduces DNA by adding nucleotides to a primer in the 5' to 3' direction, using a DNA template and magnesium as a cofactor.

Taq polymerase is valued for its stability at high temperatures, which allows it to withstand the repeated heating steps required in PCR. Its optimum activity is in the range of roughly 72–75°C, and it remains functional through the high-temperature denaturation steps that separate DNA strands during cycling. However, Taq lacks 3' to 5' exonuclease proofreading activity, contributing to a relatively higher error rate compared with high-fidelity, proofreading polymerases.

Applications of Taq polymerase include routine amplification of DNA fragments for cloning, sequencing, diagnostics, and forensic analyses. It is used in standard PCR protocols to generate sufficient DNA for downstream analysis. To improve specificity and reduce non-specific amplification, researchers employ hot-start formats and various buffer formulations. For experiments requiring higher fidelity, researchers may opt for alternative enzymes with proofreading activity, such as Pfu or Q5.

History and significance: the discovery of a heat-stable DNA polymerase from Thermus aquaticus in the late 1980s enabled automation of PCR and transformed molecular biology. The ability to perform DNA amplification on standard thermal cyclers without replenishing enzyme after each cycle contributed to the widespread adoption of PCR in research, clinical diagnostics, forensics, and applied biotechnology.