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| [[Image:Wobble.svg|thumb|right|255px|Wobble base pairs for [[inosine]] and [[guanine]]]]
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| In [[molecular biology]], a '''wobble base pair''' is a non-[[Watson-Crick base pairing]] between two [[nucleotides]] in [[RNA]] molecules. The four main wobble base pairs are [[guanine]]-[[uracil]] ('''G-U'''), [[hypoxanthine]]-uracil ('''I-U'''), hypoxanthine-[[adenine]] ('''I-A'''), and hypoxanthine-[[cytosine]] ('''I-C'''). Because hypoxanthine is the [[nucleobase]] of [[inosine]], "I" is used for the former in order to maintain consistency of nucleic acid nomenclature, which otherwise follows the names of the nucleobases (e.g., "G" for both guanine and [[guanosine]]).<ref name=Kuchin-JMBE>
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| {{cite journal
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| |url = http://jmbe.asm.org/asm/index.php/jmbe/rt/printerFriendly/267/html_111
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| |title = Covering All the Bases in Genetics: Simple Shorthands and Diagrams for Teaching Base Pairing to Biology Undergraduates
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| |last = Kuchin
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| |first = Sergei
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| |date = May 2011
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| |publisher = American Society for Microbiology
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| |journal = Journal of Microbiology & Biology Education
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| |volume = 12
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| |issue = 1
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| |doi = 10.1128/jmbe.v12i1.267
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| |accessdate = October 16, 2013
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| |quote = The correct name of the base in inosine (which is a nucleoside) is hypoxanthine, however, for consistency with the nucleic acid nomenclature, the shorthand <nowiki>[</nowiki>I<nowiki>]</nowiki> is more appropriate...}}</ref>
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| The thermodynamic stability of a wobble base pair is comparable to that of a Watson-Crick base pair. Wobble base pairs are fundamental in RNA [[secondary structure]] and are critical for the proper translation of the [[genetic code]].
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| ==tRNA wobble==
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| In the [[genetic code]], there are <math>4^3</math> = 64 possible codons (tri-[[nucleotide]] sequences). For [[translation (genetics)|translation]], each of these codons requires a [[Transfer RNA|tRNA]] molecule with a complementary [[Transfer RNA#Anticodon|anticodon]]. If each tRNA molecule paired with its complementary mRNA codon using canonical Watson-Crick base pairing, then 64 types (species) of tRNA molecule would be required. In the standard genetic code, three of these 64 codons are stop codons, which terminate translation by binding to [[release factor]]s rather than tRNA molecules, so canonical pairing would require 61 species of tRNA. Since most organisms have fewer than 45 species of tRNA,<ref>http://gtrnadb.ucsc.edu/</ref> some tRNA species must pair with more than one codon. In 1966, [[Francis Crick]] proposed the Wobble hypothesis to account for this. He postulated that the [[Directionality (molecular biology)|5']] base on the anticodon, which binds to the [[Directionality (molecular biology)|3']] base on the [[mRNA]], was not as spatially confined as the other two bases, and could, thus, have non-standard base pairing.<ref>{{cite journal|author=Crick F|title=Codon–anticodon pairing: the wobble hypothesis|journal=J Mol Biol|volume=19|issue=2|pages=548–55|year=1966|url=http://profiles.nlm.nih.gov/SC/B/C/B/S/_/scbcbs.pdf |pmid=5969078|doi=10.1016/S0022-2836(66)80022-0}}</ref> Movement ("wobble") of the base in the 5' anticodon position is necessary for this capability.<ref>{{cite book|title=Biochemistry|last1=Mathews|first1=Christopher|last2=Van Holde|first2=K.E.|last3=Appling|first3=Dean|last4=Anthony-Cahill|first4=Spencer|edition=4th|publisher=Pearson Education|location=Toronto, Canada|year=2013|isbn=978-0-13-800464-4|page=1181}}</ref>
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| As an example, [[yeast]] tRNA<sup>[[Phenylalanine|Phe]]</sup> has the anticodon 5'-GmAA-3' and can recognize the codons 5'-UUC-3' and 5'-UUU-3'. It is, therefore, possible for non-Watson–Crick base pairing to occur at the third codon position, i.e., the 3' [[nucleotide]] of the mRNA codon and the 5' nucleotide of the tRNA anticodon.<ref>{{cite journal |author=Varani G, McClain W |title=The G × U wobble base pair. A fundamental building-block of RNA structure crucial to RNA function in diverse biological systems |journal=EMBO Rep |volume=1 |issue=1 |pages=18–23 |year=2000 |url=http://www.nature.com/cgi-taf/DynaPage.taf?file=/embor/journal/v1/n1/full/embor635.html |pmid=11256617 |doi=10.1093/embo-reports/kvd001 |pmc=1083677}}</ref>
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| ===tRNA Base pairing schemes===
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| The original wobble pairing rules, as proposed by Crick. Watson-Crick base pairs are shown in '''bold''', wobble base pairs in ''italic'':
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| {| class="wikitable"
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| |-
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| !tRNA 5' anticodon base !! mRNA 3' codon base
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| |-
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| |A || '''U'''
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| |-
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| |C || '''G'''
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| |-
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| |G || '''C''' or ''U''
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| |-
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| |U || '''A''' or ''G''
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| |-
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| |I || ''A'' or ''C'' or ''U''
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| |}
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| Revised pairing rules<ref>{{cite journal |author=Murphy FV 4th, Ramakrishnan V |title=Structure of a purine-purine wobble base pair in the decoding center of the ribosome |journal=Nat Struct Mol Biol |date=Dec 2004 |volume=11 |issue=12 |pages=1251–1252 |pmid=15558050 |doi=10.1038/nsmb866 |url=http://www.nature.com/nsmb/journal/v11/n12/full/nsmb866.html}}</ref>
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| {| class="wikitable"
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| |-
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| !tRNA 5' anticodon base !! mRNA 3' codon base
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| |-
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| |G || U,C
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| |-
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| |C || G
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| |-
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| |k<sup>2</sup>C || A
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| |-
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| |A || U,C,(A),G
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| |-
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| |unmodified U || U,(C),A,G
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| |-
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| |xm<sup>5</sup>s<sup>2</sup>U,xm<sup>5</sup>Um,Um,xm<sup>5</sup>U || A,(G)
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| |-
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| |xo<sup>5</sup>U || U,A,G
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| |-
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| |I || ''A'' or ''C'' or ''U''
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| |}
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| == See also ==
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| * [[Base pair]]
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| * [[Hoogsteen base pair]]
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| ==References==
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| <references />
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| ==External links==
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| *[http://www.mun.ca/biochem/courses/3107/Lectures/Topics/tRNA.html tRNA, the Adaptor Hypothesis and the Wobble Hypothesis]
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| *[http://www.ncbi.nlm.nih.gov/books/bv.fcgi?rid=mboc4.figgrp.1058 Wobble base-pairing between codons and anticodons]
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| {{DEFAULTSORT:Wobble Base Pair}}
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| [[Category:Nucleic acids]]
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| [[Category:Protein biosynthesis]]
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| {{genetics-stub}}
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