Editing Plant virus (section)

=== 5' Cap ===

For [[Translation (biology)|translation]] to occur, [[eukaryotic]] mRNAs require a [[5' Cap]] structure. This means that viruses must also have one. This normally consists of 7MeGpppN where N is normally [[adenine]] or [[guanine]]. The viruses encode a protein, normally a [[replicase]], with a [[methyltransferase]] activity to allow this.

Some viruses are cap-snatchers. During this process, a <sup>7m</sup>G-capped host mRNA is recruited by the viral transcriptase complex and subsequently cleaved by a virally encoded endonuclease. The resulting capped leader RNA is used to prime transcription on the viral genome.<ref>{{cite journal |last1=Duijsings |display-authors=etal |year=2001|title=''In vivo'' analysis of the TSWV cap-snatching mechanism: single base complementarity and primer length requirements |journal=The EMBO Journal |volume=20 |issue=10|pages=2545–2552 |doi=10.1093/emboj/20.10.2545 |pmid=11350944 |pmc=125463}}</ref>

However some plant viruses do not use cap, yet translate efficiently due to cap-independent translation enhancers present in 5' and 3' untranslated regions of viral mRNA.<ref>{{cite journal |last1=Kneller |first1=Elizabeth L. Pettit |last2=Rakotondrafara |first2=Aurélie M. |last3=Miller |first3=W. Allen |title=Cap-independent translation of plant viral RNAs |journal=Virus Research |date=July 2006 |volume=119 |issue=1 |pages=63–75 |doi=10.1016/j.virusres.2005.10.010 |pmid=16360925 |pmc=1880899}}</ref>