DNA ligase 8697 225584487 2008-07-14T12:40:31Z CarinaT 3636119 iwfix {{Unreferenced|date=February 2007}} {{protein | Name = ligase I, DNA, ATP-dependent | caption = DNA ligase repairing chromosomal damage. | image = DNA Repair.jpg | width = 200 | HGNCid = 6598 | Symbol = LIG1 | AltSymbols = | EntrezGene = 3978 | OMIM = 126391 | RefSeq = NM_000234 | UniProt = P18858 | PDB = | ECnumber = 6.5.1.1 | Chromosome = 19 | Arm = | Band = | LocusSupplementaryData = }} {{protein | Name = ligase III, DNA, ATP-dependent | caption = | image = | width = 250px | HGNCid = 6600 | Symbol = LIG3 | AltSymbols = | EntrezGene = 3980 | OMIM = 600940 | RefSeq = NM_002311 | UniProt = P49916 | PDB = | ECnumber = | Chromosome = 17 | Arm = q | Band = 11.2 | LocusSupplementaryData = -q12 }} {{protein | Name = ligase IV, DNA, ATP-dependent | caption = | image = | width = | HGNCid = 6601 | Symbol = LIG4 | AltSymbols = | EntrezGene = 3981 | OMIM = 601837 | RefSeq = NM_002312 | UniProt = P49917 | PDB = | ECnumber = | Chromosome = 13 | Arm = q | Band = 33 | LocusSupplementaryData = -q34 }} In [[molecular biology]], '''DNA ligase''' is a particular type of [[ligase]] ({{EC number|6.5.1.1}}) that can link together two [[DNA]] strands that have single-strand breaks (a break in both complementary strands of DNA). The alternative, a double-strand break, is fixed by a different type of DNA ligase using the [[Complementary DNA|complementary strand]] as a template but still requires DNA ligase to create the final [[phosphodiester bond]] to fully repair the DNA. DNA ligase has applications in both [[DNA repair]] and [[DNA replication]] (see [[DNA ligase#Mammalian ligases|''Mammalian ligases'']]). In addition, DNA ligase has extensive use in molecular biology laboratories for [[Genetic recombination]] experiments (see [[DNA ligase#Applications in molecular biology research|''Applications in molecular biology research'']]). ==Ligase mechanism== The mechanism of DNA ligase is to form two [[covalent]] [[phosphodiester bonds]] between [[3' end|3' hydroxyl ends]] of one [[nucleotide]] with the [[5' end|5' phosphate end]] of another. ATP is not required for the ligase reaction. A pictorial example of how a ligase works (with [[DNA end|sticky end]]s): [[Image:Ligation.svg|400px]] Ligase will also work with [[DNA end|blunt end]]s, although higher enzyme concentrations and different reaction conditions are required. ==Mammalian ligases==<!-- This section is linked from [[DNA ligase]] --> In mammals, there are four specific types of ligase. *DNA ligase I: ligates [[Okazaki fragments]] during [[lagging strand]] [[DNA replication]] and some [[recombinant]] fragments. *DNA ligase II: alternatively [[splice]]d form of DNA ligase III found in non-dividing cells. *DNA ligase III: [[protein complex|complexes]] with [[DNA repair]] [[protein]] [[XRCC1]] to aid in sealing [[DNA repair|base excision]] [[mutations]] and recombinant fragments. *DNA ligase IV: complexes with [[XRCC4]]. It catalyzes the final step in the [[non-homologous end joining]] DNA double-strand break repair pathway. It is also required for [[V(D)J recombination]], the process which generates diversity in [[immunoglobulin]] and [[T-cell receptor]] loci during [[immune system]] development. ==Applications in molecular biology research==<!-- This section is linked from [[DNA ligase]] --> DNA ligases have become an indispensable tool in modern molecular biology research for generating [[recombinant]] DNA sequences. For example, DNA ligases are used with [[restriction enzyme]]s to insert DNA fragments, often [[genes]], into [[plasmid]]s. One vital, and often tricky, aspect to performing successful recombination experiments involving ligase is controlling the optimal temperature. Most experiments use T4 DNA Ligase (isolated from [[Enterobacteria phage T4|bacteriophage T4]]) which is most active at 25°C. However in order to perform successful ligations, the optimal enzyme temperature needs to be balanced with the [[melting temperature]] T<sub>m</sub> (also the [[annealing temperature]]) of the DNA fragments being ligated. If the ambient temperature exceeds T<sub>m</sub>, [[Homologous chromosome|homologous pairing]] of the sticky ends will not occur because the high temperature disrupts [[hydrogen bonding]]. The shorter the DNA fragments, the lower the T<sub>m</sub>. Thus for sticky ends (overlaps) less than ten [[base pairs]] long, ligation experiments are performed at very low temperatures (~4-8°C) for a long period of time (often overnight). The common commercially available DNA ligases were originally discovered in [[Enterobacteria phage T4|bacteriophage T4]], ''[[E. coli]]'' and other [[bacteria]]. == See also == *[[DNA end]] *[[Lagging strand]] *[[DNA replication]] *[[Okazaki fragment]] *[[DNA Polymerase]] ==External links== *[http://nist.rcsb.org/pdb/molecules/pdb55_1.html DNA Ligase: PDB molecule of the month] *[http://www.bio.davidson.edu/Courses/Molbio/MolStudents/spring2003/Weber/ligation.html Davidson College General Information on Ligase] *[http://openwetware.org/wiki/DNA_ligation OpenWetWare DNA Ligation Protocol] {{Ligases}} {{DNA replication}} [[Category:EC 6.5]] [[Category:molecular biology]] [[Category:DNA replication]] [[de:Ligasen]] [[es:ADNligasa]] [[fr:ADN ligase]] [[it:DNA ligasi (ATP)]] [[nl:DNA-ligase]] [[ja:DNAリガーゼ]] [[pl:Ligaza DNA]] [[pt:DNA ligase]] [[zh:DNA黏合酶]]