Taq polymerase
From Wikipedia, the free encyclopedia
Taq polymerase ("Taq Pol," or simply "Taq") is a thermostable polymerase used in polymerase chain reaction to check for the presence or absence of a gene by amplifying a DNA fragment. It replaced E.coli DNA polymerase in PCR because of the temperature conditions of PCR. First isolated from Thermus aquaticus (hence the abbreviation "Taq"), a bacterium that lives in hot springs and hydrothermal vents, Taq was identified as the first polymerase able to withstand the denaturing conditions required during PCR. Its enzymatic halflife (at 95 degrees Celsius) is 40 min.
One of Taq polymerases' drawbacks is its low replication fidelity since it lacks a 3' to 5' exonuclease proofreading mechanism. Commercially sold Taq DNA polymerase has an error rate of one in 10,000 nucleotides and typically produces 16% of mutated 1kb (kilobasepair) PCR products in a reaction. It can amplify a 1kb strand of DNA in roughly 30 seconds at 72°C. Despite its error rate, Taq DNA polymerase can still be used in experiments where an identical genetic sequence is required (such as in molecular cloning). The resulting vector plus insert has to be controlled by DNA sequencing anyway.
Taq DNA polymerase also yields fragments with A (Adenine) overhangs. This is particularly useful in 'TA Cloning,' whereby a cloning vector (such as a plasmid) is used which has T (Thymine) overhangs which complement with the A overhangs of the PCR Product, thus increasing the ligation efficiency.
Pfu DNA polymerase is often used instead of, or in conjunction with, Taq polymerase. This enzyme is more thermostable and proofreads DNA, resulting in a lower error rate.
Leading commercial suppliers of Taq DNA Polymerase include Promega, Roche and Invitrogen.
[edit] See also
