Structural and mechanistic conservation in DNA ligases

DNA ligases are enzymes required for the repair, replication and recombinat ion of DNA. DNA ligases catalyse the formation of phosphodiester bonds at s ingle-strand breaks in double-stranded DNA. Despite their occurrence in all organisms, DNA ligases show a wide diversity of amino acid sequences, mole cular sizes and properties. The enzymes fall into two groups based on their cofactor specificity, those requiring NAD(+) for activity and those requir ing ATP. The eukaryotic, viral and archael bacteria encoded enzymes all req uire ATP. NAD(+)-requiring DNA ligases have only been found in prokaryotic organisms. Recently, the crystal structures of a number of DNA ligases have been reported. It is the purpose of this review to summarise the current k nowledge of the structure and catalytic mechanism of DNA ligases.