TOPO cloning is a molecular biology technique in which DNA fragments are cloned into specific vectors without the requirement for DNA ligases. For TOPO TA cloning, the Taq polymerase has a nontemplate-dependent terminal transferase activity that adds a single deoxyadenosine (A) to the 3'-end of the PCR products. This characteristic is exploited in TOPO-cloning For Blunt End TOPO cloning, the recipient vector does not have overhangs and blunt-ended DNA fragments can be cloned.