Calf-intestinal alkaline phosphatase (CIAP/CIP) is an enzyme that catalyzes the 5' phosphate group's removal, dephosphorylation, from DNA . This enzyme is frequently used in DNA sub-cloning, because DNA fragments that lack the 5' phosphoryl termini cannot self-ligate . This is used to prevent recircularization and religation of linearized cloning vehicle DNA by removing phosphate groups from both 5´-termini. Preventing self-ligation is important both in improving the yield of properly ligated product and in reducing the background of improperly self-ligated contaminant.