Digested DNA typically possesses a 5’ phosphate group that is required for ligation. In order to prevent self-ligation, the 5' phosphate can be removed prior to ligation. Dephosphorylation of the 5’ end prohibits self-ligation, enabling the researcher to manipulate the DNA as desired before re-ligating. Generally, it is a good idea to dephosphorylate the linearized vector to facilitate ligation of recombinant DNA molecules. In fact, vector self-ligation increases the background activity of the cloning process. Dephosphorylation can be accomplished using any of a number of phosphatases, including Shrimp Alkaline Phosphatase (rSAP) (NEB #M0371), Calf Intestinal Alkaline Phosphatase (CIP) (NEB #M0290) and Antarctic Phosphatase (NEB #M0289).