Taq polymerase
/ TACK polymerase /
PCR needs to heat DNA to almost boiling, over and over, to pull the strands apart. The problem: a normal copying enzyme would be cooked and destroyed by that heat in the first cycle. The solution came from an unlikely place — a microbe living in scalding hot springs. Taq polymerase is the heat-proof DNA-copying enzyme that makes PCR practical.
Taq is short for Thermus aquaticus, a bacterium discovered in the hot springs of Yellowstone that thrives near boiling water. Its DNA polymerase evolved to stay folded and working at those temperatures, surviving the roughly 95 degree Celsius denaturation step of every PCR cycle. Like other DNA polymerases, it reads a single-stranded template, needs a primer to start, and adds new nucleotides one at a time in the 5'-to-3' direction, matching A to T and G to C. Because it tolerates the heat, you can add it once at the start and let it run through all 30-plus cycles, rather than reopening the tube to add fresh enzyme each round.
Before Taq, PCR was a clumsy chore: each heating step killed the enzyme, so you had to add more by hand every cycle. Taq turned PCR into a single closed-tube reaction you can automate in a thermal cycler — the real reason PCR became a routine tool. One honest caveat: ordinary Taq lacks proofreading, so it makes occasional copying errors. For applications that demand a faithful sequence, labs use proofreading 'high-fidelity' polymerases (such as Pfu) instead.
A scientist sets up a PCR with template, primers, the four nucleotide building blocks, a magnesium-containing buffer, and one dose of Taq. The tube goes into the cycler and runs unattended for hours — the heat-proof Taq survives every 95 degree melt and keeps copying right through to the end.
A heat-stable enzyme survives every denaturation step.
Standard Taq has no proofreading, so it makes occasional errors; when an exact sequence matters, use a high-fidelity proofreading polymerase instead. Taq's discovery is also a classic case of basic curiosity about extreme-environment microbes paying off unexpectedly.