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Taq polymerase



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.

Additional recommended knowledge

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

  1. ^ a b Chien A, Edgar DB, Trela JM (1976). "Deoxyribonucleic acid polymerase from the extreme thermophile Thermus aquaticus". J. Bacteriol 174: 1550-1557. PMID 8432.
  2. ^ Lawyer FC, Stoffel S, Saiki RK, Chang SY, Landre PA, Abramson RD, Gelfand DH (1993). "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. 2: 275-287. PMID 8324500.
  3. ^ Tindall KR, Kunkel TA. (1988). "Fidelity of DNA synthesis by the Thermus aquaticus DNA polymerase". Biochemistry 27: 6008-6013. PMID 2847780.
 
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Taq_polymerase". A list of authors is available in Wikipedia.
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