[dē¦äk·sē‚rī·bō·nü¦klē·ik ¦as·əd ′lī‚gās] (biochemistry) An enzyme which joins the ends of two deoxyribonucleic acid chains by catalyzing the synthesis of a phosphodiester bond between a 3′-hydroxyl group at the end of one chain and a 5′-phosphate at the end of the other.