Biology:Outron
An outron is a nucleotide sequence at the 5' end of the primary transcript of a gene that is removed by a special form of RNA splicing during maturation of the final RNA product.[1] Whereas intron sequences are located inside the gene, outron sequences lie outside the gene.[2]
Characteristics
The outron is an intron-like sequence possessing similar characteristics such as the G+C content[3] and a splice acceptor site that is the signal for trans-splicing.[4][5] Such a trans-splice site is essentially defined as an acceptor (3') splice site without an upstream donor (5') splice site.
In eukaryotes such as euglenozoans, dinoflagellates, sponges, nematodes, cnidarians, ctenophores, flatworms, crustaceans, chaetognaths, rotifers, and tunicates, the length of spliced leader (SL) outrons range from 30 to 102 nucleotides (nt), with the SL exon length ranging from 16 to 51 nt, and the full SL RNA length ranging from 46 to 141 nt.[3]
Processing
In standard cis-splicing, the donor splice site in upstream position is required together with an acceptor site located on downstream position on the same pre-RNA molecule. By contrast, the SL trans-splicing relies on a 3' acceptor splice site on the outron, and a 5' donor splice site (GU dinucleotide) located on a separate RNA molecule, the SL RNA.[3] Moreover, the outron of the premature mRNA contains a branchpoint adenosine — followed by a downstream polypyrimidine tract — which interacts with the intron-like portion of the SL RNA to form a 'Y' branched byproduct, reminiscent of the lasso structure formed during intron splicing. Nuclear machinery then resolves this 'Y' branching structure by trans-splicing the SL RNA sequence to the 3′ trans-splice acceptor site (AG dinucleotide) of the pre-mRNA.[2]
When outrons are processed, the SL exon is trans-spliced to distinct, unpaired, downstream acceptor sites adjacent to each open reading frame of the polycistronic pre-mRNA, leading to distinct mature capped transcripts. [6][7][8]
See also
- Biology:Exon – A region of a transcribed gene present in the final functional mRNA molecule
- Biology:Messenger RNA – RNA that is read by the ribosome to produce a protein
References
- ↑ Conrad, Richard; Fen Liou, Ruey; Blumenthal, Thomas (1993-02-25). "Functional analysis of a C. elegans trans-splice acceptor" (in en). Nucleic Acids Research 21 (4): 913–919. doi:10.1093/nar/21.4.913. ISSN 0305-1048. PMID 8451190.
- ↑ 2.0 2.1 Stover, Nicholas A.; Kaye, Michelle S.; Cavalcanti, Andre R. O. (2006-01-10). "Spliced leader trans-splicing" (in English). Current Biology 16 (1): R8–R9. doi:10.1016/j.cub.2005.12.019. ISSN 0960-9822. PMID 16401417.
- ↑ 3.0 3.1 3.2 Lasda, Erika L.; Blumenthal, Thomas (2011-05-01). "Trans-splicing" (in en). Wiley Interdisciplinary Reviews: RNA 2 (3): 417–434. doi:10.1002/wrna.71. PMID 21957027.
- ↑ "Oxford reference — Outron". https://www.oxfordreference.com/view/10.1093/oi/authority.20110803100257646.
- ↑ "The MISO Sequence Ontology Browser — Outron (SO:0001475)". http://www.sequenceontology.org/browser/current_svn/term/SO:0001475.
- ↑ Clayton, Christine E. (2002-04-15). "Life without transcriptional control? From fly to man and back again" (in en). The EMBO Journal 21 (8): 1881–1888. doi:10.1093/emboj/21.8.1881. ISSN 1460-2075. PMID 11953307.
- ↑ Blumenthal, Thomas; Gleason, Kathy Seggerson (February 2003). "Caenorhabditis elegans operons: form and function" (in en). Nature Reviews Genetics 4 (2): 110–118. doi:10.1038/nrg995. ISSN 1471-0056. PMID 12560808.
- ↑ "Evolutionary Insights into RNA trans-Splicing in Vertebrates". Genome Biology and Evolution 8 (3): 562–77. March 2016. doi:10.1093/gbe/evw025. PMID 26966239.
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