Taq polymerase

Taq polymerase is a thermostable DNA polymerase named after the thermophilic bacterium Thermus aquaticus from which it was originally isolated. 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. 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.

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. 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.