What Is DNA Polymerase

The most commonly used reagent in polymerase chain reaction (PCR) studies is called Taq DNA, pronounced "tack-DNA." It is a thermodynamically stable DNA polymerase that is made from a strain of E. coli bacteria that carries the Taq DNA polymerase gene. It was originally isolated in 1965 from a bacterium called thermus aquaticus, a bacterium that lives in hydrothermal vents and hot springs. Taq DNA is an enzyme that can withstand the high temperatures required during PCR studies. Taq's optimum activity temperature is 75 to 80 degrees Centigrade. At 72 degrees Centigrade it can replicate a 1,000 base pair strand of DNA.

It is not ideal, however, because its replication fidelity is relatively low, with an error rate of about 1 in 9,000 nucleotides. There have been other DNA polymerases isolated from other heat-loving bacteria that are used in PCR experiments with higher fidelity amplification. 

Before Taq DNA polymerase, the denaturing reagent used in PCR would be inactivated after only one round of DNA replication, when the samples had to be heated again. But now, with thermodynamically stable Taq DNA polymerase, technicians do not have to add new enzyme to the PCR reaction in the thermo cycling. Since a single closed tube can be used to carry out the entire process, Taq DNA polymerase is a substance that has helped multiply the practical uses for PCR.

In 1989, Science Magazine declared Taq polymerase the "Molecule of the Year," the very first substance to achieve that designation. By the early 1990s, PCR with Taq DNA polymerase was being used in basic research, forensics, and clinical testing.