DNA ligase
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{{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]]