Contains 500 Weiss units, at 1–3u/μl. One Weiss unit=67 Cohesive End Ligation Units. T4 DNA Ligase catalyzes the joining of 2 DNA strands between the 5´-P and the 3´-OH groups of adjacent nucleotides in either cohesive-ended or blunt-ended configuration. The enzyme has been shown to catalyze the joining of RNA to either a DNA or RNA strand in a duplex molecule but will not join single-stranded nucleic acids.