Editing Trans-splicing (section)

== SL ''trans''-splicing ==
Spliced leader (SL) ''trans''-splicing is used by certain microorganisms, notably protists of the [[Kinetoplastea]] class to express genes. In these organisms, a capped splice leader RNA is transcribed, and simultaneously, genes are transcribed in long polycistrons.<ref>{{cite journal | vauthors = Campbell DA, Sturm NR, Yu MC | title = Transcription of the kinetoplastid spliced leader RNA gene | journal = Parasitology Today | volume = 16 | issue = 2 | pages = 78–82 | date = February 2000 | pmid = 10652494 | doi = 10.1016/s0169-4758(99)01545-8 }}</ref> The capped splice leader is ''trans''-spliced onto each gene to generate monocistronic capped and polyadenylated transcripts.<ref name=pmid14555465>{{cite journal | vauthors = Liang XH, Haritan A, Uliel S, Michaeli S | title = trans and cis splicing in trypanosomatids: mechanism, factors, and regulation | journal = Eukaryotic Cell | volume = 2 | issue = 5 | pages = 830–40 | date = October 2003 | pmid = 14555465 | pmc = 219355 | doi = 10.1128/EC.2.5.830-840.2003 }}</ref> These early-diverging eukaryotes use few [[intron]]s, and the spliceosome they possess show some unusual variations in their structure assembly.<ref name=pmid14555465/><ref>{{cite journal | vauthors = Günzl A | title = The pre-mRNA splicing machinery of trypanosomes: complex or simplified? | journal = Eukaryotic Cell | volume = 9 | issue = 8 | pages = 1159–70 | date = August 2010 | pmid = 20581293 | pmc = 2918933 | doi = 10.1128/EC.00113-10 }}</ref> They also possess multiple [[eIF4E]] isoforms with specialized roles in capping.<ref>{{cite journal | vauthors = Freire ER, Sturm NR, Campbell DA, de Melo Neto OP | title = The Role of Cytoplasmic mRNA Cap-Binding Protein Complexes in Trypanosoma brucei and Other Trypanosomatids | journal = Pathogens | volume = 6 | issue = 4 | pages = 55 | date = October 2017 | pmid = 29077018 | pmc = 5750579 | doi = 10.3390/pathogens6040055 | doi-access = free }}</ref> The spliced leader sequence is highly conserved in lower species that undergo trans-splicing. Such as trypanosomes. While the spliced leader's role is not known in the cell, it's thought to be involved in translation initiation. In C''.elegans'', the splicing of the sequence leader occurs close to the initiation codon. Some scientists also suggest the sequence is required for cell viability. In Ascaris, the spliced leader sequence is needed to the RNA gene can be transcribed. The Spliced leader sequence may be responsible for initiation, mRNA localization, and translation initiation or inhibition.<ref name=":0" />

Some other eukaryotes, notably among [[dinoflagellates]], [[sponges]], [[nematodes]], [[cnidarians]], [[ctenophores]], [[flatworms]], [[crustaceans]], [[chaetognaths]], [[rotifers]], and [[tunicates]] also use more or less frequently the SL ''trans''-splicing.<ref name="Lei2016"/><ref name="Lasda2011">{{cite journal | vauthors = Lasda EL, Blumenthal T | title = Trans-splicing | journal = Wiley Interdisciplinary Reviews: RNA | volume = 2 | issue = 3 | pages = 417–34 | date = 2011-05-01 | pmid = 21957027 | doi = 10.1002/wrna.71 | s2cid = 209567118 }}</ref> In the tunicate ''[[Ciona intestinalis]]'', the extent of SL ''trans''-splicing is better described by a quantitative view recognising frequently and infrequently ''trans''-spliced genes rather than a binary and conventional categorisation of ''trans''-spliced versus non-''trans''-spliced genes.<ref name="Matsumoto2010">{{cite journal | vauthors = Matsumoto J, Dewar K, Wasserscheid J, Wiley GB, Macmil SL, Roe BA, Zeller RW, Satou Y, Hastings KE | display-authors = 6 | title = High-throughput sequence analysis of Ciona intestinalis SL trans-spliced mRNAs: alternative expression modes and gene function correlates | journal = Genome Research | volume = 20 | issue = 5 | pages = 636–45 | date = May 2010 | pmid = 20212022 | pmc = 2860165 | doi = 10.1101/gr.100271.109 }}</ref>

The SL ''trans''-splicing functions in the resolution of [[polycistronic]] transcripts of [[operon]]s into individual 5'-capped mRNAs. This processing is achieved when the [[outron]]s are ''trans''-spliced to unpaired, downstream acceptor sites adjacent to cistron [[open reading frames]].<ref name="Clayton2002">{{Cite journal|last=Clayton|first=Christine E.|date=2002-04-15|title=Life without transcriptional control? From fly to man and back again|journal=The EMBO Journal|language=en|volume=21|issue=8|pages=1881–1888|doi=10.1093/emboj/21.8.1881|issn=1460-2075|pmc=125970|pmid=11953307}}</ref><ref name="Blumenthal2003">{{Cite journal|last1=Blumenthal|first1=Thomas|last2=Gleason|first2=Kathy Seggerson|date=February 2003|title=''Caenorhabditis elegans'' operons: form and function|journal=Nature Reviews Genetics|language=en|volume=4|issue=2|pages=110–118|doi=10.1038/nrg995|pmid=12560808|s2cid=9864778|issn=1471-0056}}</ref>