Editing Intron (section)

{{Short description|Specific base pair sequences within a gene}}
{{About||the interferon-based drug used in viral and cancer treatments|Intron A|the album by [[LCD Soundsystem]]|Introns (album)}}

An '''intron''' is any [[Nucleic acid sequence|nucleotide sequence]] within a [[gene]] that is not expressed or operative in the final RNA product. The word ''intron'' is derived from the term ''<u>intr</u>agenic regi<u>on</u>'', i.e., a region inside a gene.<ref name="Gilbert1978">"The notion of the cistron [i.e., gene] ... must be replaced by that of a transcription unit containing regions which will be lost from the mature messenger – which I suggest we call introns (for intragenic regions) – alternating with regions which will be expressed – exons." (Gilbert 1978) {{cite journal | vauthors = Gilbert W | title = Why genes in pieces? | journal = Nature | volume = 271 | issue = 5645 | pages = 501 | date = February 1978 | pmid = 622185 | doi = 10.1038/271501a0 | s2cid = 4216649 | author-link = Walter Gilbert | bibcode = 1978Natur.271..501G | doi-access = free }}</ref> The term ''intron'' refers to both the DNA sequence within a gene and the corresponding RNA sequence in RNA [[Transcription (genetics)|transcripts]].<ref>{{cite journal | vauthors = Kinniburgh AJ, Mertz JE, Ross J | title = The precursor of mouse beta-globin messenger RNA contains two intervening RNA sequences | journal = Cell | volume = 14 | issue = 3 | pages = 681–693 | date = July 1978 | pmid = 688388 | doi = 10.1016/0092-8674(78)90251-9 | s2cid = 21897383 }}</ref> The non-intron sequences that become joined by this RNA processing to form the mature RNA are called [[exon]]s.<ref name="Lewin1987">{{Cite book | vauthors = Lewin B |title=Genes |pages=159–179, 386 |date=1987 |publisher=Wiley |isbn=0-471-83278-2 |edition=3rd |location=New York |oclc=14069165}}</ref>

Introns are found in the genes of most eukaryotes and many eukaryotic viruses, and they can be located in both protein-coding genes and genes that function as RNA ([[Non-coding RNA|noncoding genes]]). There are four main types of introns: tRNA introns, group I introns, group II introns, and spliceosomal introns (see below). Introns are rare in Bacteria and Archaea (prokaryotes).