A taq enzyme is a bacterial enzyme that functions in the manufacture of deoxyribonucleic acid (DNA). The ability of the enzyme to function at higher temperatures than other similarly functioning bacterial enzymes has made it valuable in the polymerase chain reaction.

The moniker taq denotes the origin of the enzyme. The enzyme is produced by a bacterium known as Thermus aquaticus. This bacterium was discovered by Thomas Brock in the mid 1970s in the nearly boiling waters of Mushroom pool, a hot spring in Yellowstone National Park

Taq is a DNA polymerase. The enzyme manufactures a strand of DNA that is complimentary to a single strand of DNA. All bacteria possess DNA polymerase. The reason that the taq polymerase has become so significant to biotechnological processes is because of the resistance of the enzyme to heat. A molecular biology technique known as the polymerase chain reaction relies upon the exposure of DNA to heat in order to separate the two strands of the double helix. Taq can then use both of the single strands as templates for the manufacture of two new strands of DNA. To perform this function, the polymerase is able to recognize the particular building block, or nucleotide, on the DNA single strand and then position a nucleotide that is the complimentary match to the particular target. Binding of the two nucleotides occurs. The polymerase can then move on to the next nucleotide and the process is repeated. When the DNA mixture is allowed to cool the matching strands link together forming two double stranded helices of DNA. If this process is repeated many times, a huge number of copies of the target region of DNA can be manufactured. The heat resistance of taq allows the enzyme to function in the temperature conditions that keep the DNA strands apart from each other. The DNA polymerase from other bacteria, for example from the bacterium Escherichia coli, do not function nearly as efficiently in the polymerase chain reaction as the taq polymerase of Thermus aquaticus.

Since the discovery of taq enzyme and the development of the polymerase chain reaction, the importance of the enzyme to molecular biology research and commercial applications of biotechnology have soared. Taq polymerase is widely used in the molecular diagnosis of maladies and in forensics ("DNA fingerprinting"). These and other applications of taq have spawned an industry worth hundreds of millions of dollars annually.