After digestion by restriction endonucleases, DNA strands can be joined again by

In mammals, after many Okazaki fragments are generated, the replication complex begins to remove the RNA primers, to fill in the gaps left by their removal with the proper base-paired deoxynucleotide, and then to seal the fragments of newly synthesized DNA by enzymes referred to as DNA ligases. DNA ligase Seals the single strand nick between the nascent chain and Okazaki fragments on the lagging strand.Ref.: Harpers Illustrated Biochemistry; 30th edition; page no: 383