Endocyclase N15 (Protelomerase N15) catalyzes formation of covalent links between complementary 5′- and 3′- ends (clamps DNA strands together) and forms exonuclease-protected hairpin ends at specific double-stranded DNA recognition sites. Generates covalent clamps between two complementary DNA strands on one or on both ends. Converts PCR products to linear plasmids with capped “hairpin” ends. Converts circular plasmid DNA to linear plasmid DNA. Protects PCR-amplified, processed DNA from exonuclease attack and digestion.