Editing Nucleotide base (section)

==Artificial nucleobases==
{{Main|Nucleic acid analogue}}
A vast number of nucleobase analogues exist.
The most common applications are used as fluorescent probes, either directly or indirectly, such as [[aminoallyl nucleotide]], which are used to label cRNA or cDNA in [[microarrays]]. Several groups are working on alternative "extra" base pairs to extend the genetic code, such as [[isoguanine]] and [[isocytosine]] or the fluorescent [[2-amino-6-(2-thienyl)purine]] and [[pyrrole-2-carbaldehyde]].<ref name="pmid15051811">{{cite journal|vauthors=Johnson SC, Sherrill CB, Marshall DJ, Moser MJ, Prudent JR|date=2004|title=A third base pair for the polymerase chain reaction: inserting isoC and isoG|journal=Nucleic Acids Research|volume=32|issue=6|pages=1937–41|doi=10.1093/nar/gkh522|pmc=390373|pmid=15051811}}</ref><ref>{{cite journal|vauthors=Kimoto M, Mitsui T, Harada Y, Sato A, Yokoyama S, Hirao I|year=2007|title=Fluorescent probing for RNA molecules by an unnatural base-pair system|journal=Nucleic Acids Research|volume=35|issue=16|pages=5360–69|doi=10.1093/nar/gkm508|pmc=2018647|pmid=17693436}}</ref>

In medicine, several [[nucleoside analogue]]s are used as anticancer and antiviral agents. The viral polymerase incorporates these compounds with non-canonical bases. These compounds are activated in the cells by being converted into nucleotides; they are administered as [[nucleoside]]s as charged nucleotides cannot easily cross cell membranes.{{Citation needed|date=April 2012}} At least one set of new base pairs has been announced as of May 2014.<ref>{{cite journal | vauthors = Malyshev DA, Dhami K, Lavergne T, Chen T, Dai N, Foster JM, Corrêa IR, Romesberg FE | title = A semi-synthetic organism with an expanded genetic alphabet | journal = Nature | volume = 509 | issue = 7500 | pages = 385–8 | date = May 2014 | pmid = 24805238 | pmc = 4058825 | doi = 10.1038/nature13314 | bibcode = 2014Natur.509..385M }}</ref>