DNA ligase

DNA ligase is an enzyme that seals breaks in DNA by catalyzing phosphodiester bonds between adjacent nucleotides. It joins DNA fragments during replication, repair, and recombination.

Phosphodiester bond: A covalent bond linking the 3′ carbon of one sugar to the 5′ phosphate of another in nucleic acids. Ligase forms this bond to close a break in a DNA strand.
DNA replication: The cellular process that copies a DNA molecule before cell division. Ligase joins Okazaki fragments on the lagging strand during replication.
DNA: A nucleic-acid molecule that stores hereditary information in most organisms. Ligase acts on DNA’s sugar-phosphate backbone.
RNA ligase: An enzyme that joins RNA ends by forming phosphodiester bonds. RNA ligases perform a similar reaction but act on RNA substrates.
Martin Gellert: An American molecular biologist who discovered DNA ligase in 1967. Gellert identified an enzyme that could join DNA strands, revealing a key step in replication.
DNA nick: A break in one strand of double-stranded DNA that leaves the complementary strand intact. A nick with adjacent 3′-hydroxyl and 5′-phosphate ends is ligase’s direct substrate.
Okazaki fragment: A short DNA segment synthesized discontinuously on the lagging strand during replication. Ligase seals the nicks between these fragments after primer removal and gap filling.
Nucleotide: A molecule composed of a nitrogenous base, a sugar, and one or more phosphate groups. DNA’s nucleotide arrangement supplies the neighboring ends that ligase connects.
DNA topoisomerase: An enzyme that changes DNA topology by transiently breaking and rejoining DNA strands. Topoisomerases reseal DNA breaks they create, but alter DNA winding rather than simply joining fragments.
Weiss and Richardson DNA ligase: The ATP-dependent DNA ligase activity purified from bacteriophage-infected Escherichia coli by Robert Weiss and Charles Richardson. Their characterization established a distinct ligase activity alongside Gellert’s discovery.

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