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An intron is any nucleotide sequence within a gene that is not expressed or operative in the final RNA product. The word intron is derived from the term intragenic region, i.e., a region inside a gene.[1] The term intron refers to both the DNA sequence within a gene and the corresponding RNA sequence in RNA transcripts.[2] The non-intron sequences that become joined by this RNA processing to form the mature RNA are called exons.[3]
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 (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).
- ^ "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) Gilbert W (February 1978). "Why genes in pieces?". Nature. 271 (5645): 501. Bibcode:1978Natur.271..501G. doi:10.1038/271501a0. PMID 622185. S2CID 4216649.
- ^ Kinniburgh AJ, Mertz JE, Ross J (July 1978). "The precursor of mouse beta-globin messenger RNA contains two intervening RNA sequences". Cell. 14 (3): 681–693. doi:10.1016/0092-8674(78)90251-9. PMID 688388. S2CID 21897383.
- ^ Lewin B (1987). Genes (3rd ed.). New York: Wiley. pp. 159–179, 386. ISBN 0-471-83278-2. OCLC 14069165.