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The successful incorporation of a third base pair is a significant breakthrough toward the goal of greatly expanding the number of [[amino acid]]s which can be encoded by DNA, from the existing 20 amino acids to a theoretically possible 172, thereby expanding the potential for living organisms to produce novel [[protein]]s.<ref name="Fikes"/> The artificial strings of DNA do not encode for anything yet, but scientists speculate they could be designed to manufacture new proteins which could have industrial or pharmaceutical uses.<ref name="Pollack">{{cite news| url=https://www.nytimes.com/2014/05/08/business/researchers-report-breakthrough-in-creating-artificial-genetic-code.html?hpw&rref=business&_r=0| title=Scientists Add Letters to DNA's Alphabet, Raising Hope and Fear |last=Pollack| first=Andrew| name-list-style = vanc | date=May 7, 2014| work=New York Times| access-date=8 May 2014}}</ref> Experts said the synthetic DNA incorporating the unnatural base pair raises the possibility of life forms based on a different DNA code.<ref name = "fox">{{cite news| url=http://www.foxnews.com/health/2014/05/08/scientists-create-organism-using-artificial-dna/| title=Scientists create first living organism containing artificial DNA| date=May 8, 2014| work=The Wall Street Journal |publisher=Fox News| access-date=8 May 2014}}</ref><ref name = "Pollack" />
== Variant of base pairing ==
[[File:Hoogsteen_Watson_Crick_pairing-en.svg|thumb|251x251px|Chemical structures for Watson-Crick and Hoogsteen A•T and G•C+ base pairs.<ref name="Nikolova">{{cite journal|author1=Evgenia N. Nikolova|author2=Eunae Kim|author3=Abigail A. Wise|author4=Patrick J. O'Brien|author5=Ioan Andricioaei|author6=Hashim M. Al-Hashimi|year=2011|title=Transient Hoogsteen base pairs in canonical duplex DNA|journal=Nature|volume=470|issue=7335|pages=498–502|bibcode=2011Natur.470..498N|doi=10.1038/nature09775|pmc=3074620|pmid=21270796}}</ref>]]
In addition to the canonical pairing, some conditions can also favour base-pairing with alternative base orientation, and number and geometry of hydrogen bonds. These pairings are accompanied by alterations to the local backbone shape. The most common of these is [[Hoogsteen base pairing]] (typically written as A•U/T and G•C). Hoogsteen base pairs can exist in some DNA sequences (e.g. CA and TA dinucleotides) in dynamic equilibrium with standard Watson–Crick pairing.<ref name="Nikolova2">{{cite journal|author1=Evgenia N. Nikolova|author2=Eunae Kim|author3=Abigail A. Wise|author4=Patrick J. O'Brien|author5=Ioan Andricioaei|author6=Hashim M. Al-Hashimi|year=2011|title=Transient Hoogsteen base pairs in canonical duplex DNA|journal=Nature|volume=470|issue=7335|pages=498–502|bibcode=2011Natur.470..498N|doi=10.1038/nature09775|pmc=3074620|pmid=21270796}}</ref> They have also been observed in some protein–DNA complexes.<ref name="Aishima">{{cite journal|author=Jun Aishima, Rossitza K. Gitti, Joyce E. Noah, Hin Hark Gan, [[Tamar Schlick]], Cynthia Wolberger|year=2002|title=A Hoogsteen base pair embedded in undistorted B‐DNA|journal=Nucleic Acids Res|volume=30|issue=23|pages=5244–5252|doi=10.1093/nar/gkf661|pmc=137974|pmid=12466549}}</ref>
==Length measurements==<!-- This section is linked from [[KB]] -->
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