Molecular markers
Polymerase chain reaction
Taq polymerase

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

Revised: 4 June 2018, last major update July 2010

Copyright: (c) 2008-2018, PathologyOutlines.com, Inc.

PubMed Search: Taq polymerase[TI]

Table of Contents
Definition / general
Cite this page: Shackelford, R.E. Taq polymerase. PathologyOutlines.com website. http://www.pathologyoutlines.com/topic/molecularpathtaqpolymerase.html. Accessed August 16th, 2018.
Definition / general
  • 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 90 °C 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:
    1. Enzyme works best at 75 - 80 °C, allowing the elongation step to occur at temperatures which make non-Watson-Crick base paring a rare event
    2. Its half life at 95 °C is over 40 minutes
    3. At 72 °C 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