Image 7: PCR products obtained using Taq Polymerase
(Obtained from http://en.wikipedia.org/wiki/Polymerase_chain_reaction)
In
the lab, Taq polymerase is used almost exclusively in polymerase chain
reaction (PCR) for amplifying DNA fragments. Commercially sold Taq
polymerase contains all the essential components for PCR reaction.
Taq DNA polymerase has several unique advantages that make it highly practical for use in the lab. One of the most important properties of Taq is its stability at high temperatures. In fact, Taq polymerase has an optimum temperature activity of about 75ºC. Most primers used in PCR bind more specifically at higher temperatures, and so using Taq polymerase at these temperatures gives a higher yield of the desired product with less nonspecific amplification.
Taq also has a high processivity rate; it replicates DNA rather quickly. At 72ºC, Taq has a processivity of 50-60 nucleotides per second. Most other enzymes are much slower than Taq. Thus, Taq can provide a reasonably accurate copy within a few minutes.
One of the major drawbacks of Taq though its its low replication fidelity, meaning that it has a relatively higher error rate. This is because of the lack of a 3' -> 5' exonuclease proofreading ability. Thus, when very specified amplification is desired, scientists often turn to other high fidelity polymerases. But for most PCR products, the error rate of Taq polymerase is negligible, and its processivity is ideal.
The lack of the 3' -> 5' proof reading ability also causes Taq to add a single 3' nucleotide on both strands of every amplified product. This extension permits direct cloning of the PCR product using various cloning vectors.
All these qualities have led Taq polymerase to be the most commonly used polymerase for PCR and is a must have in almost every lab!
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Taq DNA polymerase has several unique advantages that make it highly practical for use in the lab. One of the most important properties of Taq is its stability at high temperatures. In fact, Taq polymerase has an optimum temperature activity of about 75ºC. Most primers used in PCR bind more specifically at higher temperatures, and so using Taq polymerase at these temperatures gives a higher yield of the desired product with less nonspecific amplification.
Taq also has a high processivity rate; it replicates DNA rather quickly. At 72ºC, Taq has a processivity of 50-60 nucleotides per second. Most other enzymes are much slower than Taq. Thus, Taq can provide a reasonably accurate copy within a few minutes.
One of the major drawbacks of Taq though its its low replication fidelity, meaning that it has a relatively higher error rate. This is because of the lack of a 3' -> 5' exonuclease proofreading ability. Thus, when very specified amplification is desired, scientists often turn to other high fidelity polymerases. But for most PCR products, the error rate of Taq polymerase is negligible, and its processivity is ideal.
The lack of the 3' -> 5' proof reading ability also causes Taq to add a single 3' nucleotide on both strands of every amplified product. This extension permits direct cloning of the PCR product using various cloning vectors.
All these qualities have led Taq polymerase to be the most commonly used polymerase for PCR and is a must have in almost every lab!
Back