DNA ligase enzyme mechanism

DNA Ligase play important role in DNA replication, repair mechanism , recombinant DNA technoly and clonning purpose.

Mechanism of DNA Ligase enzyme

1) Addition of AMP:transfer of AMP from ATP Or NAD to the lysine residue in active site of the Ligase enzyme.

2) Activation of 5' phosphate:
Enzyme transfer AMP to the 5' phosphate present in the Nick region of the DNA.

3) Nucleiophilic attack of 3'OH
3'OH attacks the 5 'phosphate attached with AMP and it leads to removal of AMP from 5' phosphate.

4) Formation of phosphodiester bond:
Phosphodiester bond is formed and DNA is sealed.

Different types of DNA Ligase is present:

Ecoli DNA Ligase uses NAD for the formation of phosphodiester bond.

T4 Ligase is isolated from bacteriophase and eukaryotic DNA Ligase uses ATP as energy source.

mammals contain different types of DNA Ligase

DNA Ligase I works on lagging strand. ribonuclease H removes RNA primer from okazaki fragment of the DNA and DNA is sealed.

DNA Ligase III complex with XRCC1 and works on nucleotide excision repair mechanism.

DNA Ligase IV complex XRCC4. IT works on non homologous end joining and also takes part in Vdj recombination.