ligaser

Ligases are a family of enzymes that catalyze the joining of two substrate molecules by forming a new covalent bond, typically using energy from ATP, NAD+, or another donor. The reaction is essential for building and maintaining biomolecules and cellular structures. Most ligases act on macromolecules such as nucleic acids, proteins, or aminoacyl-tRNA complexes.

DNA ligases seal single-strand breaks, or nicks, in the sugar-phosphate backbone during DNA replication and repair. Eukaryotic and archaeal ligases mainly rely on ATP, while many bacterial ligases use NAD+ as the energy cofactor. Beyond DNA, ligases participate in RNA processing (RNA ligases) and in protein modification pathways such as ubiquitin ligases (E3 enzymes) that catalyze the transfer of ubiquitin to substrate proteins. Other enzymes classified as ligases include aminoacyl-tRNA synthetases, which ligate amino acids to tRNA during protein synthesis; these enzymes are technically ligases in the IUBMB classification.

In laboratory settings, ligases are essential tools. T4 DNA ligase and other DNA ligases are used to join DNA fragments in cloning and plasmid construction, while RNA ligases enable RNA ligation. Proper regulation and localization of ligase activity are important in cells to prevent erroneous joins and to ensure correct progression of replication, repair, and remodeling processes.