DNA ligase

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DNA ligase is an enzyme that anneals DNA strands together. It forms a phosphodiester bond between the complementary bases on two separate DNA strands. ATP is hydrolysed in order to release a pyrophosphate, and the AMP that is formed attaches to the 5' end of the donor. The pyrophosphate bond activates the 5' end and a phosphodiester bond forms between the 5' phosphate and the 3' hydroxyl. DNA ligase is a crucial element in recombinant technology[1].

DNA ligase is an enzyme used for the ligation of blunt-ended and sticky ended recombinant fragments or Okazaki fragments. With blunt ends a higher enzyme concentration and different reaction conditions are required in comparison to when DNA ligase acts on sticky ends. DNA ligase works by repairing breaks in the sugar phosphate backbone in DNA by creating a covalent bond between adjoining nucleotides (between the 3’hydroxyl group of one DNA molecule with the 5’phosphoryl group of another)[2]. In eukaryotes DNA ligase I family members play the major role. The enzyme has a fundamental role in genetic engineering such as recombinant plasmid formation or Polymerase Chain Reaction[3].

Image to demonstrate how DNA ligase catalyses the formation of phosphodiester bonds between sticky ends of DNA fragments to form a longer fragment of DNA


  1. Alberts, Bruce. Molecular Biology of the Cell. 5th ed. New York: Garland Science, 2008, p 273
  2. Hartl D. L., Ruvolo M. (2012), Genetics: Analysis of genes and genomes, Eight Edition, Jones and Bartlett learning (Chapter 2 DNA Structure and Genetic Variation) p440-42
  3. Berg, J.M., Tymoczko, J.L. and Stryer, L. (2012). Biochemistry, 7 th Edition, New York, W.H.Freeman and Co Ltd. p152-153
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