Supplier Page from New England Biolabs for T4 DNA Ligase
Unit Definition:One NEB unit is defined as the amount of enzyme required to give 50% ligation of HindIII fragments of Lambda DNA in 30 minutes at 16°C in 20 µl of the above assay mixture and a 5´ DNA terminiconcentration of 0.12 µM (300 µg/ml).