Q5® High-Fidelity DNA Polymerase is an ultra high-fidelity, thermostable DNA polymerase with 3´→ 5´ exonuclease activity, fused to a processivity-enhancing Sso7d domain to support robust DNA amplification. With an error rate ~280-fold lower than that of Taq DNA Polymerase, Q5 High-Fidelity DNA Polymerase is ideal for cloning and can be used for long or difficult amplicons. The Q5 High-Fidelity 2X Master Mix offers robust, high-fidelity performance in a convenient master mix format. The mix contains dNTPs, Mg++ and a proprietary broad-use buffer requiring only the addition of primers and DNA template for robust amplification, regardless of GC content. When used at the recommended 1X final concentration, the Q5 High-Fidelity Master Mix contains 2 mM MgCl2.