Q.The enzyme which is purified from calf intestine :

Alkaline phosphatase, purified from calf intestine, prevents vector self-ligation in gene cloning.

When a plasmid vector is cut open with a restriction enzyme to accept a foreign DNA insert, its two linearised ends still carry 5'-phosphate groups, which allows DNA ligase to simply reseal the vector back on itself (self-ligation/recircularisation) instead of incorporating the desired insert, lowering cloning efficiency. To prevent this, molecular biologists treat the cut vector with calf intestinal alkaline phosphatase (CIAP), an enzyme purified from calf (bovine) intestinal tissue that catalyses the hydrolytic removal of the 5'-phosphate groups from the vector's ends. Without a 5'-phosphate, DNA ligase cannot reseal the vector on itself, but it can still join the vector's 3'-OH ends to a phosphorylated insert, greatly increasing the proportion of recombinant (insert-containing) plasmids recovered. This dephosphorylation role is distinct from res …