DNA ligase

A DNA ligase is an enzyme which can repair DNA by creating new covalent bonds between two pieces ofDNA.

Like all enzymes, the DNA ligases are proteins with an active site enabling the enzymatic reaction and a donor (a nucleotide OH group) and acceptor (a phosphate group from another nucleotide) molecular recognition sites which make the reaction specific.

The role of the DNA ligases is to covalently bind two pieces of DNA together. Using a molecule of DNA that provides them with the necessary energy, the DNA ligases create a phosphodiester bond between two nucleotides, whether these belong to a single stranded or a double stranded DNA.

There are different type of DNA ligases which have roles in different biological process:

• DNA ligase 1 is involved in DNA replication when the new strands produced (the Okasaki fragments) must be connected together.
• The other types of DNA ligases (2, 3, or 4) are involved in the repair of DNA breaks.