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Molecular Pathology

Polymerase Chain Reaction

Taq Polymerase


Author: Rodney E. Shackelford, D.O., Ph.D. (see Reviewers page)

Revised: 8 July 2010, last major update July 2010

Copyright: (c) 2008-2010, PathologyOutlines.com, Inc.




● Initially the Klenow fragment from the E. coli DNA polymerase I was used in PCR reactions

While the Klenow fragment worked in PCR, it rapidly denatured at the 90C or higher temperatures required for denaturation, requiring the addition of new Klenow polymerase after every denaturation step

The need to open the reaction chamber with every PCR thermocycle made PCR cumbersome and greatly increased the chances for contamination with unwanted DNA

The solution to this problem came from the discovery and cloning of a thermostable DNA polymerase from the thermophilic bacterium Thermus aquaticus

The polymerase, known as the Taq polymerase, has many attributes that are well suited for PCR:

(a) the enzyme works best at 75-80C, allowing the elongation step to occur at temperatures which make non-Watson-Crick base paring a rare event

(b) its half-life at 95C is over 40 minutes

(c) at 72C it can add 1,000 nucleoside triphosphates to a growing DNA strand

● Most PCR reactions done with Taq can be completely closed through all the thermocycles

Taq lacks 3' to 5' exonuclease proofreading activity, allowing a roughly 1 per 9,000 error rate in nucleoside triphosphate incorporation

Additionally, Taq often adds an adenine to the end of its polymerase reaction (sometimes used to facilitate TA cloning)

Taq was named The Molecule of the Year by Science in 1989


End of Molecular Pathology > Polymerase Chain Reaction > Taq polymerase



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