''Trans''-splicing is a special form of
RNA processing where
exon
An exon is any part of a gene that will form a part of the final mature RNA produced by that gene after introns have been removed by RNA splicing. The term ''exon'' refers to both the DNA sequence within a gene and to the corresponding sequence ...
s from two different primary
RNA transcripts are joined end to end and
ligated. It is usually found in
eukaryote
The eukaryotes ( ) constitute the Domain (biology), domain of Eukaryota or Eukarya, organisms whose Cell (biology), cells have a membrane-bound cell nucleus, nucleus. All animals, plants, Fungus, fungi, seaweeds, and many unicellular organisms ...
s and mediated by the
spliceosome, although some bacteria and archaea also have "half-genes" for
tRNA
Transfer ribonucleic acid (tRNA), formerly referred to as soluble ribonucleic acid (sRNA), is an adaptor molecule composed of RNA, typically 76 to 90 nucleotides in length (in eukaryotes). In a cell, it provides the physical link between the gene ...
s.
Genic ''trans''-splicing
Whereas "normal"
(''cis''-)splicing processes a single molecule, ''trans''-splicing generates a single RNA transcript from multiple separate
pre-mRNA
A primary transcript is the single-stranded ribonucleic acid (RNA) product synthesized by Transcription (genetics), transcription of DNA, and processed to yield various mature RNA products such as mRNAs, tRNAs, and rRNAs. The primary transcript ...
s. This phenomenon can be exploited for molecular therapy to address mutated gene products. Genic trans-splicing allows variability in RNA diversity and increases proteome complexity.
Oncogenesis
While some fusion transcripts occur via ''trans''-splicing in normal human cells,
''trans''-splicing can also be the mechanism behind certain oncogenic
fusion transcripts.
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. The capped splice leader is ''trans''-spliced onto each gene to generate monocistronic capped and polyadenylated transcripts.
These early-diverging eukaryotes use few
intron
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."The notion of the cistron .e., gen ...
s, and the spliceosome they possess show some unusual variations in their structure assembly.
[ They also possess multiple eIF4E isoforms with specialized roles in capping. 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.]sponges
Sponges or sea sponges are primarily marine invertebrates of the animal phylum Porifera (; meaning 'pore bearer'), a basal clade and a sister taxon of the diploblasts. They are sessile filter feeders that are bound to the seabed, and ar ...
, nematodes
The nematodes ( or ; ; ), roundworms or eelworms constitute the phylum Nematoda. Species in the phylum inhabit a broad range of environments. Most species are free-living, feeding on microorganisms, but many are parasitic. Parasitic worms (he ...
, cnidarians
Cnidaria ( ) is a phylum under kingdom Animalia containing over 11,000 species of aquatic invertebrates found both in fresh water, freshwater and marine environments (predominantly the latter), including jellyfish, hydroid (zoology), hydroids, ...
, ctenophores
Ctenophora (; : ctenophore ) is a phylum of marine invertebrates, commonly known as comb jellies, that marine habitats, inhabit sea waters worldwide. They are notable for the groups of cilia they use for swimming (commonly referred to as "combs ...
, flatworms, crustaceans
Crustaceans (from Latin meaning: "those with shells" or "crusted ones") are invertebrate animals that constitute one group of Arthropod, arthropods that are traditionally a part of the subphylum Crustacea (), a large, diverse group of mainly aquat ...
, chaetognaths, rotifers
The rotifers (, from Latin 'wheel' and 'bearing'), sometimes called wheel animals or wheel animalcules, make up a phylum (Rotifera ) of microscopic and near-microscopic pseudocoelomate animals.
They were first described by Rev. John Harris ...
, and tunicates also use more or less frequently the SL ''trans''-splicing.
Mechanism
Trans-splicing is characterized by the joining of two separate exons transcribed RNAs. The signal for this splicing is the outron at the 5’ end of the mRNA, in the absence of a functional 5’ splice site upstream. When the 5’ outron in spliced, the 5’ splice site of the spliced leader RNA is branched to the outron and forms an intermediate.
Trans-splicing between sense and anti-sense strands
As a result of the sense strand undergoing transcription, a pre-mRNA is formed that complements the sense strand. The anti-sense strand is also transcribed resulting in a complementary pre-mRNA strand. The exons from the two transcripts are spliced together to form a chimeric mRNA.
Alternative Trans-splicing
Alternative trans-splicing includes intragenic trans-splicing and intergenic trans-splicing. Intragenic trans-splicing involves duplication of exons in the pre-mRNA. Intergenic trans-splicing is characterized by the splicing together of exons formed form the pre-mRNA of two different genes, resulting in trans-genic mRNA.
See also
* Chimera (EST)
References
Further reading
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RNA
Spliceosome
RNA splicing