Editing DNA ligase (section)

== Research applications ==
{{main|Ligation (molecular biology) }}
DNA ligases have become indispensable tools 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.

Controlling the optimal temperature is a vital aspect of performing efficient recombination experiments involving the ligation of cohesive-ended fragments.  Most experiments use T4 DNA Ligase (isolated from [[Enterobacteria phage T4|bacteriophage T4]]), which is most active at 37&nbsp;°C.<ref name="Baneyx_1993">{{cite book | vauthors = Baneyx F, Lucotte G | title = Introduction to Molecular Cloning Techniques | publisher = John Wiley & Sons | location = Chichester | year = 1993 | page = 156 | isbn = 978-0-471-18849-0 }}</ref>  However, for optimal ligation efficiency with cohesive-ended fragments ("sticky ends"), the optimal enzyme temperature needs to be balanced with the [[DNA melting|melting temperature]] T<sub>m</sub> of the sticky ends being ligated,<ref name="Tabor_2001">{{cite journal | vauthors = Tabor S | title = DNA ligases | journal = Current Protocols in Molecular Biology | volume = Chapter 3 | pages = Unit 3.14 | date = May 2001 | pmid = 18265223 | doi = 10.1002/0471142727.mb0314s08 | isbn = 978-0-471-14272-0 | s2cid = 23944826 }}</ref> the [[Homologous chromosome|homologous pairing]] of the sticky ends will not be stable because the high temperature disrupts [[hydrogen bonding]]. A ligation reaction is most efficient when the sticky ends are already stably annealed, and disruption of the annealing ends would therefore result in low ligation efficiency. The shorter the [[DNA end#Overhangs and sticky ends|overhang]], the lower the T<sub>m</sub>.

Since blunt-ended DNA fragments have no cohesive ends to anneal, the melting temperature is not a factor to consider within the normal temperature range of the ligation reaction. The limiting factor in blunt end ligation is not the activity of the ligase but rather the number of alignments between DNA fragment ends that occur.  The most efficient ligation temperature for blunt-ended DNA would therefore be the temperature at which the greatest number of alignments can occur.  The majority of blunt-ended ligations are carried out at 14-25&nbsp;°C overnight.  The absence of stably annealed ends also means that the ligation efficiency is lowered, requiring a higher ligase concentration to be used.<ref name="Tabor_2001"/>

A novel use of DNA ligase can be seen in the field of nano chemistry, specifically in DNA origami. &nbsp;DNA based self-assembly principles have proven useful for organizing nanoscale objects, such as biomolecules, nanomachines, nanoelectronic and photonic component. Assembly of such nano structure requires the creation of an intricate mesh of DNA molecules. Although DNA self-assembly is possible without any outside help using different substrates such as provision of catatonic surface of Aluminium foil, DNA ligase can provide the enzymatic assistance that is required to make DNA lattice structure from DNA over hangs.<ref name="pmid28189681">{{cite journal | vauthors = Bhanjadeo MM, Nayak AK, Subudhi U | title = Surface-assisted DNA self-assembly: An enzyme-free strategy towards formation of branched DNA lattice | journal = Biochemical and Biophysical Research Communications | volume = 485 | issue = 2 | pages = 492–498 | year = 2017 | pmid = 28189681 | doi = 10.1016/j.bbrc.2017.02.024 }}</ref>