Editing RNA splicing (section)

==Biochemical mechanism==
[[File:RNA splicing reaction.svg|thumb|400px|Diagram illustrating the two-step biochemistry of splicing]]
Spliceosomal splicing and self-splicing involve a two-step biochemical process.  Both steps involve [[transesterification]] reactions that occur between RNA nucleotides.  tRNA splicing, however, is an exception and does not occur by transesterification.<ref name=abelson1998>{{cite journal | vauthors = Abelson J, Trotta CR, Li H | title = tRNA splicing | journal = The Journal of Biological Chemistry | volume = 273 | issue = 21 | pages = 12685–12688 | date = May 1998 | pmid = 9582290 | doi = 10.1074/jbc.273.21.12685 | doi-access = free }}</ref>

Spliceosomal and self-splicing transesterification reactions occur via two sequential transesterification reactions.  First, the 2'OH of a specific ''branchpoint'' nucleotide within the intron, defined during spliceosome assembly, performs a [[nucleophilic attack]] on the first nucleotide of the intron at the 5' splice site, forming the ''lariat intermediate''.  Second, the 3'OH of the released 5' exon then performs a nucleophilic attack at the first nucleotide following the last nucleotide of the intron at the 3' splice site, thus joining the exons and releasing the intron lariat.<ref name=fica2013>{{cite journal | vauthors = Fica SM, Tuttle N, Novak T, Li NS, Lu J, Koodathingal P, Dai Q, Staley JP, Piccirilli JA | display-authors = 6 | title = RNA catalyses nuclear pre-mRNA splicing | journal = Nature | volume = 503 | issue = 7475 | pages = 229–234 | date = November 2013 | pmid = 24196718 | pmc = 4666680 | doi = 10.1038/nature12734 | bibcode = 2013Natur.503..229F }}</ref>