Tth DNA Ligase (2500 U)

This thermostable DNA ligase from QIAGEN is isolated from an Escherichia coli strain carrying the Thermus thermophilus DNA ligase gene. The enzyme catalyzes the NAD-dependent formation of phosphodiester bonds between adjacent 3'-hydroxyl and 5'-phosphate termini in double-stranded DNA, and is not active against single-stranded DNA, RNA, or blunt-ended DNA.

The enzyme is stable and active across an optimum ligation temperature range of 45–65°C, which is 7–10°C higher than that of T4 DNA ligase, with the final reaction temperature determined by the Tm of the substrates. High ligation temperatures help eliminate non-specific ligation. One unit of Tth DNA Ligase catalyzes the ligation of 50% of the cos sites present in 1 µg of bacteriophage lambda DNA in 1 minute at 45°C, and is equivalent to 15 cohesive end units (CEU).

Quality control testing confirms the product is free of detectable DNase, exonuclease, and endonuclease activities. The enzyme is supplied in a buffer containing 50 mM Tris-HCl (pH 7.5), 100 mM NaCl, 0.1 mM EDTA, 0.1% Triton X-100, 1 mM DTT, and 50% glycerol. Recommended applications include ligase chain reaction (LCR) and other thermostable ligation protocols; cofactors and temperature should be optimized according to the manufacturer's instructions and the product stored at -20°C using nuclease-free consumables.