Editing Intron (section)

=== Spliceosomal introns ===
{{see also|RNA splicing#Spliceosomal|}}
Nuclear pre-mRNA introns (spliceosomal introns) are characterized by specific intron sequences located at the boundaries between introns and exons.<ref>{{cite journal | vauthors = Padgett RA, Grabowski PJ, Konarska MM, Seiler S, Sharp PA | title = Splicing of messenger RNA precursors | journal = Annual Review of Biochemistry | volume = 55 | pages = 1119–1150 | year = 1986 | pmid = 2943217 | doi = 10.1146/annurev.bi.55.070186.005351 }}</ref> These sequences are recognized by spliceosomal RNA molecules when the splicing reactions are initiated.<ref>{{cite journal | vauthors = Guthrie C, Patterson B | title = Spliceosomal snRNAs | journal = Annual Review of Genetics | volume = 22 | pages = 387–419 | year = 1988 | pmid = 2977088 | doi = 10.1146/annurev.ge.22.120188.002131 }}</ref> In addition, they contain a branch point, a particular nucleotide sequence near the 3' end of the intron that becomes covalently linked to the 5' end of the intron during the splicing process, generating a branched {{Clarify|post-text=(complicated jargon)|text=(''lariat'')|date=January 2024}} intron. Apart from these three short conserved elements, nuclear pre-mRNA intron sequences are highly variable. Nuclear pre-mRNA introns are often much longer than their surrounding exons.