Taq polymerase is a thermostable DNA polymerase derived from the thermophilic bacterium Thermus aquaticus, widely used to synthesize DNA in polymerase chain reaction (PCR) assays because it remains active at high temperatures.
Explanation
The discovery of Taq polymerase in the 1970s transformed molecular biology. Early PCR protocols used DNA polymerases from Escherichia coli or other mesophiles that denatured at the high temperatures needed to melt DNA strands, requiring fresh enzyme to be added after each cycle. Because Thermus aquaticus inhabits geothermal hot springs, its DNA polymerase retains activity close to 95 °C. Taq polymerase has an optimal extension temperature around 72 °C and can add about 50–100 nucleotides per second. It lacks 3′ to 5′ exonuclease proofreading activity, so its fidelity is lower than that of high fidelity enzymes, but it does have 5′ to 3′ exonuclease activity and leaves a single deoxyadenosine overhang at 3′ ends, which is useful for TA cloning. This enzyme allowed the automation of PCR, making the technique rapid and reliable. Variants such as hot start Taq polymerase use antibodies or aptamers to inhibit activity until the initial denaturation step, reducing nonspecific amplification. Taq remains a reliable enzyme for routine PCR, genotyping and diagnostic assays.
Applications in Molecular Biology
Taq polymerase is integral to many laboratory techniques. It is used in standard PCR to amplify genetic loci for cloning, sequencing and forensic analysis. Its tendency to add 3′ A overhangs enables direct TA cloning of PCR products into linearised vectors. Hot start formulations improve specificity in multiplex reactions and real time PCR assays. Although enzymes such as Pfu, Phusion and Q5 are preferred for high fidelity applications, Taq continues to be used for colony PCR, genotyping assays, environmental DNA surveys and teaching laboratories because it is robust and inexpensive.
Taq polymerase changed the polymerase chain reaction by allowing automated thermal cycling. Despite the advent of more accurate polymerases, its heat resistance, simplicity and cost effectiveness ensure its continued relevance in laboratories worldwide.
Related Terms: PCR, DNA polymerase, Thermus aquaticus, High fidelity polymerase, Amplification