DNA ligase is an enzyme that joins DNA strands through the formation of phosphodiester bonds in a process called DNA ligation. The bond in double-stranded DNA is formed by joining the 5′ phosphate and 3′ hydroxyl termini of DNA strands, using ATP as a coenzyme.
The discovery and characterization of DNA ligase enzymes occurred in 1967 by several laboratories, including Lehman, Gellert, Hurwitz, and Richardson labs. This finding was critical for developing and introducing the concept of molecular cloning and several other future biology experiments.
In organisms, DNA ligase has an essential role in DNA replication and repair. It is also a vital component of in vitro molecular biology and biotech lab assays. It is a member of the nucleotidyltransferase superfamily, along with RNA ligases and mRNA capping enzymes—all of which are essential for maintaining the structural integrity of the genome.
The importance of the enzyme in organisms can be understood by the following example.
Normal cellular processes, including replication, repair, and recombination, often leave phosphate breaks in the genome. This can cause loss of information and introduce deleterious chromosomal mutations. However, DNA ligase prevents these consequences through its enzymatic joining of nucleic acid strands.
In this article, we will cover even more functions of DNA ligase, and the enzymatic ligase reaction mechanisms in organisms and in labs.
The DNA ligase enzyme has many forms in different organisms, which include:
Unlike E. coli, T4 DNA ligase uses adenosine triphosphate (ATP) as a cofactor rather than NAD.
The enzymatic ligation reaction of DNA ligase follows three unique steps to join two strands of nucleic acid or polynucleotide chains.
After the rearrangement of the activity site’s breaks (or nicks) of DNA fragments (Okazaki fragments), the ligase reaction follows as:
Figure: An illustration of the three-step ligation reaction.
Picture Credit: GoldBio
DNA ligase has several molecular and biochemical functions inside living organisms. Furthermore, they play a huge role in lab experiments by helping biologists understand the dynamics of living bodies.
Commercially available DNA ligases have several uses in lab workflows. Of all the available DNA ligases, T4 DNA ligase is most commonly used in lab assays with other reagents, including T4 polynucleotide kinase, tris-HCL, T4 DNA Ligase Reaction Buffer, ATP, glycerol, DTT, and nuclease-free water.
Below are a few common laboratory applications of DNA ligase:
DNA ligases are involved in a variety of DNA metabolic pathways. Therefore, their genetic inactivation results in a range of phenotypes or physical appearances, such as hypersensitivity to DNA damaging agents and lethality.
Below are some common diseases caused by dysfunction or lack of DNA ligase:
The affected individual faces difficulties in keeping balance, walking, and hand-coordination. Furthermore, they might also have disturbed nerve function and involuntary movements.
DNA ligase is an enzyme that facilitates the formation of a phosphodiester bond and joins two DNA strands. Other than DNA synthesis, the enzyme has a critical role in DNA repair in all organisms.
It is also an important substrate for in vitro experiments in molecular biology labs, including molecular cloning, performing PCR reactions, and performing ligation reactions in joining blunt and cohesive ends of DNA.
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