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  • FAQ: What is the difference between the two definitions and why does NEB use the Cohesive End Unit?

    The Weiss unit is not a direct measurement of DNA ligation; it is an indirect measurement of the enzyme adenylation reaction, followed by determining ATP-PPi exchange. NEB did not think that the Weiss unit was informative enough, because the most prevalent use of T4 DNA ligase is for the ligation of DNA. As the Cohesive End Unit involves the direct measurement of DNA ligation, NEB feels that it more practically relevant.