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In molecular biology, DNA ligase is a specific type of enzyme, a ligase, () that facilitates the joining of DNA strands together by catalyzing the formation of a phosphodiester bond. It plays a role in repairing single-strand breaks in duplex DNA in living organisms, but some forms (such as DNA ligase IV) may specifically repair double-strand breaks (i.e. a break in both complementary strands of DNA). Single-strand breaks are repaired by DNA ligase using the complementary strand of the double helix as a template, with DNA ligase creating the final phosphodiester bond to fully repair the DNA. DNA ligase is used in both DNA repair and DNA replication (see ''Mammalian ligases''). In addition, DNA ligase has extensive use in molecular biology laboratories for recombinant DNA experiments (see ''Applications in molecular biology research''). Purified DNA ligase is used in gene cloning to join DNA molecules together to form recombinant DNA. ==Ligase mechanism== The mechanism of DNA ligase is to form two covalent phosphodiester bonds between 3' hydroxyl ends of one nucleotide, ("acceptor") with the 5' phosphate end of another ("donor"). ATP is required for the ligase reaction, which proceeds in three steps: # Adenylation (addition of AMP) of a lysine residue in the active center of the enzyme, pyrophosphate is released; # Transfer of the AMP to the 5' phosphate of the so-called donor, formation of a pyrophosphate bond; # Formation of a phosphodiester bond between the 5' phosphate of the donor and the 3' hydroxyl of the acceptor. Ligase will also work with blunt ends, although higher enzyme concentrations and different reaction conditions are required. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「DNA ligase」の詳細全文を読む スポンサード リンク
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