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

DNA ligase Repeat from May 10 Proteins Involved in Replication Protein Function DNA polymerases Deoxynucleotide polymerization Helicases Unwinding and separation of DNA strands Topoisomerases Relieve torsional strain that results from helicase-induced unwinding (removes supercoils) DNA primase Initiates synthesis of RNA primers Single-strand binding proteins Prevent premature reannealing of dsDNA DNA ligase Seals the single strand nick between the nascent chain and Okazaki fragments on lagging strand DNA gyrase- Its a special type of topoisomerase, has the unusual propey of being able to introduce negative supercoils into resting DNA . This facilitates the future replication of DNA because the negative supercoils neutralise the positive supercoils introduced during opening of the double helix. For understanding of the DNA replication process, flip through the pages of Lippincott Chapter on DNA replication, (p393 in 3rd edition)