"Hot Start" PCR

In certain circumstances one wishes to avoid mixing primers and target DNA at low temperatures in the presence of Taq polymerase: Taq pol is almost as efficient as Klenow pol at 37^oC; consequently, if primers mis-anneal at low temperature prior to initial template denaturation, "non-specific" amplification may occur. This may be avoided by only adding enzyme after the initial denaturation, before the reaction cools to the chosen annealing temperature. This is most conveniently done by putting wax "gems"^TM into the reaction tube after addition of everything except enzyme, then putting enzyme on top of the gem: the wax melts when the temperature reaches +/-80^oC, and the enzyme mixes with the rest of the reaction mix while the molten wax floats on top and seals the mix, taking the place of mineral oil. Information is that "gems" may be substituted by Vaseline^TM.