Taq polymerase

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Taq polymerase is a thermostable DNA polymerase named after the thermophilic bacterium Thermus aquaticus from which it was originally isolated.^[1] It is normally abbreviated to "Taq Pol," or simply "Taq", and frequently used in polymerase chain reaction.

T. aquaticus is a bacterium that lives in hot springs and hydrothermal vents, and Taq was identified as an enzyme able to withstand the protein-denaturing conditions, namely, high temperature, required during PCR.^[1] Therefore it replaced E.coli DNA polymerase in PCR. Taq's temperature optimum for activity is 75-80°C with a halflife of 9 min at 97.5°C. ^[2]

One of Taq's drawbacks is its low replication fidelity since it lacks a 3' to 5' exonuclease proofreading activity; thus it has an error rate of about one in 9,000 nucleotides. ^[3] It can amplify a 1-kb strand of DNA in roughly 30-60 seconds at 72°C. Some thermostable DNA polymerases, such as Pfu DNA polymerase that have been isolated from other thermophilic bacteria possess 3'-5'exonuclease proofreading activity and are being used instead of, or in combination with, Taq in PCR for high-fidelity amplification of DNA.

Taq yields DNA products that have A (Adenine) overhangs at their 3' ends. This is may be useful in 'TA Cloning,' whereby a cloning vector (such as a plasmid) is used which has a T (Thymine) 3' overhang, which complements with the A overhang of the PCR product, thus enabling ligation of the PCR product into the plasmid vector.

References

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1. ↑ ^{1.0 1.1} "Deoxyribonucleic acid polymerase from the extreme thermophile Thermus aquaticus J. Bacteriol 1976 ".
2. ↑ "High-level expression, purification, and enzymatic characterization of full-length Thermus aquaticus DNA polymerase and a truncated form deficient in 5' to 3' exonuclease activity PCR Methods Appl. 1993 ".
3. ↑ "Fidelity of DNA synthesis by the Thermus aquaticus DNA polymerase Biochemistry 1988 ".

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