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RNA splicing is a process in
molecular biology Molecular biology is the branch of biology that seeks to understand the molecular basis of biological activity in and between cells, including biomolecular synthesis, modification, mechanisms, and interactions. The study of chemical and phys ...
where a newly-made
precursor messenger RNA A primary transcript is the single-stranded ribonucleic acid ( RNA) product synthesized by transcription of DNA, and processed to yield various mature RNA products such as mRNAs, tRNAs, and rRNAs. The primary transcripts designated to be mRNAs ...
(pre-
mRNA In molecular biology, messenger ribonucleic acid (mRNA) is a single-stranded molecule of RNA that corresponds to the genetic sequence of a gene, and is read by a ribosome in the process of synthesizing a protein. mRNA is created during the ...
) transcript is transformed into a
mature messenger RNA Mature messenger RNA, often abbreviated as mature mRNA is a eukaryotic RNA transcript that has been spliced and processed and is ready for translation in the course of protein synthesis. Unlike the eukaryotic Eukaryotes () are organisms w ...
(
mRNA In molecular biology, messenger ribonucleic acid (mRNA) is a single-stranded molecule of RNA that corresponds to the genetic sequence of a gene, and is read by a ribosome in the process of synthesizing a protein. mRNA is created during the ...
). It works by removing all the
intron 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 ''intragenic region'', i.e. a region inside a gene."The notion of ...
s (non-coding regions of RNA) and ''splicing'' back together
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 sequen ...
s (coding regions). For nuclear-encoded genes, splicing occurs in the
nucleus Nucleus ( : nuclei) is a Latin word for the seed inside a fruit. It most often refers to: * Atomic nucleus, the very dense central region of an atom *Cell nucleus, a central organelle of a eukaryotic cell, containing most of the cell's DNA Nucl ...
either during or immediately after transcription. For those eukaryotic genes that contain introns, splicing is usually needed to create an mRNA molecule that can be translated into protein. For many eukaryotic introns, splicing occurs in a series of reactions which are catalyzed by the spliceosome, a complex of small nuclear ribonucleoproteins ( snRNPs). There exist self-splicing introns, that is,
ribozyme Ribozymes (ribonucleic acid enzymes) are RNA molecules that have the ability to catalyze specific biochemical reactions, including RNA splicing in gene expression, similar to the action of protein enzymes. The 1982 discovery of ribozymes demons ...
s that can catalyze their own excision from their parent RNA molecule. The process of transcription, splicing and
translation Translation is the communication of the meaning of a source-language text by means of an equivalent target-language text. The English language draws a terminological distinction (which does not exist in every language) between ''transla ...
is called
gene expression Gene expression is the process by which information from a gene is used in the synthesis of a functional gene product that enables it to produce end products, protein or non-coding RNA, and ultimately affect a phenotype, as the final effect. T ...
, the
central dogma of molecular biology The central dogma of molecular biology is an explanation of the flow of genetic information within a biological system. It is often stated as "DNA makes RNA, and RNA makes protein", although this is not its original meaning. It was first stated by ...
.


Splicing pathways

Several methods of RNA splicing occur in nature; the type of splicing depends on the structure of the spliced intron and the
catalyst Catalysis () is the process of increasing the rate of a chemical reaction by adding a substance known as a catalyst (). Catalysts are not consumed in the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recyc ...
s required for splicing to occur.


Spliceosomal complex


Introns

The word ''intron'' is derived from the terms ''intragenic region'', and ''intracistron'', that is, a segment of DNA that is located between two exons of a
gene In biology, the word gene (from , ; "...Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''birth'' or ''gender'') can have several different meanings. The Mendelian gene is a b ...
. The term intron refers to both the DNA sequence within a gene and the corresponding sequence in the unprocessed RNA transcript. As part of the RNA processing pathway, introns are removed by RNA splicing either shortly after or concurrent with transcription. Introns are found in the genes of most organisms and many viruses. They can be located in a wide range of genes, including those that generate
proteins Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respo ...
,
ribosomal RNA Ribosomal ribonucleic acid (rRNA) is a type of non-coding RNA which is the primary component of ribosomes, essential to all cells. rRNA is a ribozyme which carries out protein synthesis in ribosomes. Ribosomal RNA is transcribed from riboso ...
(rRNA), and
transfer RNA Transfer RNA (abbreviated tRNA and formerly referred to as sRNA, for soluble RNA) is an adaptor molecule composed of RNA, typically 76 to 90 nucleotides in length (in eukaryotes), that serves as the physical link between the mRNA and the amino ...
(tRNA). Within introns, a donor site (5' end of the intron), a branch site (near the 3' end of the intron) and an acceptor site (3' end of the intron) are required for splicing. The splice donor site includes an almost invariant sequence GU at the 5' end of the intron, within a larger, less highly conserved region. The splice acceptor site at the 3' end of the intron terminates the intron with an almost invariant AG sequence. Upstream (5'-ward) from the AG there is a region high in
pyrimidine Pyrimidine (; ) is an aromatic, heterocyclic, organic compound similar to pyridine (). One of the three diazines (six-membered heterocyclics with two nitrogen atoms in the ring), it has nitrogen atoms at positions 1 and 3 in the ring. The othe ...
s (C and U), or polypyrimidine tract. Further upstream from the polypyrimidine tract is the branchpoint, which includes an adenine nucleotide involved in lariat formation. The
consensus sequence In molecular biology and bioinformatics, the consensus sequence (or canonical sequence) is the calculated order of most frequent residues, either nucleotide or amino acid, found at each position in a sequence alignment. It serves as a simplified r ...
for an intron (in IUPAC nucleic acid notation) is: G-G- utG-U-R-A-G-U (donor site) ... intron sequence ... Y-U-R-A-C (branch sequence 20-50 nucleotides upstream of acceptor site) ... Y-rich-N-C-A-G- utG (acceptor site). However, it is noted that the specific sequence of intronic splicing elements and the number of nucleotides between the branchpoint and the nearest 3’ acceptor site affect splice site selection. Also, point mutations in the underlying DNA or errors during transcription can activate a ''cryptic splice site'' in part of the transcript that usually is not spliced. This results in a
mature messenger RNA Mature messenger RNA, often abbreviated as mature mRNA is a eukaryotic RNA transcript that has been spliced and processed and is ready for translation in the course of protein synthesis. Unlike the eukaryotic Eukaryotes () are organisms w ...
with a missing section of an exon. In this way, a
point mutation A point mutation is a genetic mutation where a single nucleotide base is changed, inserted or deleted from a DNA or RNA sequence of an organism's genome. Point mutations have a variety of effects on the downstream protein product—consequence ...
, which might otherwise affect only a single amino acid, can manifest as a deletion or truncation in the final protein.


Formation and activity

Splicing is catalyzed by the spliceosome, a large RNA-protein complex composed of five small nuclear ribonucleoproteins ( snRNPs). Assembly and activity of the spliceosome occurs during transcription of the pre-mRNA. The RNA components of snRNPs interact with the intron and are involved in catalysis. Two types of spliceosomes have been identified (major and minor) which contain different snRNPs. *The major spliceosome splices introns containing GU at the 5' splice site and AG at the 3' splice site. It is composed of the U1, U2, U4, U5, and U6 snRNPs and is active in the nucleus. In addition, a number of proteins including U2 small nuclear RNA auxiliary factor 1 (U2AF35), U2AF2 (U2AF65) and SF1 are required for the assembly of the spliceosome. The spliceosome forms different complexes during the splicing process: :*Complex E :**The U1 snRNP binds to the GU sequence at the 5' splice site of an intron; :** Splicing factor 1 binds to the intron branch point sequence; :**U2AF1 binds at the 3' splice site of the intron; :** U2AF2 binds to the polypyrimidine tract; :*Complex A (pre-spliceosome) :**The U2 snRNP displaces SF1 and binds to the branch point sequence and ATP is hydrolyzed; :*Complex B (pre-catalytic spliceosome) :**The U5/U4/U6 snRNP trimer binds, and the U5 snRNP binds exons at the 5' site, with U6 binding to U2; :*Complex B* :**The U1 snRNP is released, U5 shifts from exon to intron, and the U6 binds at the 5' splice site; :*Complex C (catalytic spliceosome) :**U4 is released, U6/U2 catalyzes transesterification, making the 5'-end of the intron ligate to the A on intron and form a lariat, U5 binds exon at 3' splice site, and the 5' site is cleaved, resulting in the formation of the lariat; :*Complex C* (post-spliceosomal complex) :**U2/U5/U6 remain bound to the lariat, and the 3' site is cleaved and exons are ligated using ATP hydrolysis. The spliced RNA is released, the lariat is released and degraded, and the snRNPs are recycled. :This type of splicing is termed ''canonical splicing'' or termed the ''lariat pathway'', which accounts for more than 99% of splicing. By contrast, when the intronic flanking sequences do not follow the GU-AG rule, ''noncanonical splicing'' is said to occur (see "minor spliceosome" below). *The
minor spliceosome The minor spliceosome is a ribonucleoprotein complex that catalyses the removal ( splicing) of an atypical class of spliceosomal introns (U12-type) from messenger RNAs in some clades of eukaryotes. This process is called noncanonical splicing, as op ...
is very similar to the major spliceosome, but instead it splices out rare introns with different splice site sequences. While the minor and major spliceosomes contain the same U5 snRNP, the minor spliceosome has different but functionally analogous snRNPs for U1, U2, U4, and U6, which are respectively called U11, U12, U4atac, and U6atac.


Recursive splicing

In most cases, splicing removes introns as single units from precursor
mRNA In molecular biology, messenger ribonucleic acid (mRNA) is a single-stranded molecule of RNA that corresponds to the genetic sequence of a gene, and is read by a ribosome in the process of synthesizing a protein. mRNA is created during the ...
transcripts. However, in some cases, especially in mRNAs with very long introns, splicing happens in steps, with part of an intron removed and then the remaining intron is spliced out in a following step. This has been found first in the ''
Ultrabithorax Ultrabithorax (Ubx) is a homeobox gene found in insects, and is used in the regulation of patterning in morphogenesis. There are many possible products of this gene, which function as transcription factors. Ubx is used in the specification of se ...
'' (''Ubx'') gene of the fruit fly, ''
Drosophila melanogaster ''Drosophila melanogaster'' is a species of fly (the taxonomic order Diptera) in the family Drosophilidae. The species is often referred to as the fruit fly or lesser fruit fly, or less commonly the " vinegar fly" or "pomace fly". Starting with ...
'', and a few other ''Drosophila'' genes, but cases in humans have been reported as well.


Trans-splicing

Trans-splicing is a form of splicing that removes introns or outrons, and joins two exons that are not within the same RNA transcript. Trans-splicing can occur between two different endogenous
pre-mRNA A primary transcript is the single-stranded ribonucleic acid ( RNA) product synthesized by transcription of DNA, and processed to yield various mature RNA products such as mRNAs, tRNAs, and rRNAs. The primary transcripts designated to be mRNAs ...
s or between an endogenous and an exogenous (such as from viruses) or artificial RNAs.


Self-splicing

Self-splicing occurs for rare introns that form a
ribozyme Ribozymes (ribonucleic acid enzymes) are RNA molecules that have the ability to catalyze specific biochemical reactions, including RNA splicing in gene expression, similar to the action of protein enzymes. The 1982 discovery of ribozymes demons ...
, performing the functions of the spliceosome by RNA alone. There are three kinds of self-splicing introns, ''
Group I Group 1 may refer to: * Alkali metal, a chemical element classification for Alkali metal * Group 1 (racing), a historic (until 1981) classification for Touring car racing, applied to standard touring cars. Comparable to modern FIA Group N * Group On ...
'', '' Group II'' and '' Group III''. Group I and II introns perform splicing similar to the spliceosome without requiring any protein. This similarity suggests that Group I and II introns may be evolutionarily related to the spliceosome. Self-splicing may also be very ancient, and may have existed in an
RNA world The RNA world is a hypothetical stage in the evolutionary history of life on Earth, in which self-replicating RNA molecules proliferated before the evolution of DNA and proteins. The term also refers to the hypothesis that posits the existen ...
present before protein. Two transesterifications characterize the mechanism in which group I introns are spliced: # 3'OH of a free guanine nucleoside (or one located in the intron) or a nucleotide cofactor (GMP, GDP, GTP) attacks phosphate at the 5' splice site. # 3'OH of the 5' exon becomes a nucleophile and the second transesterification results in the joining of the two exons. The mechanism in which group II introns are spliced (two transesterification reaction like group I introns) is as follows: # The 2'OH of a specific adenosine in the intron attacks the 5' splice site, thereby forming the ''lariat'' # The 3'OH of the 5' exon triggers the second transesterification at the 3' splice site, thereby joining the exons together.


tRNA splicing

tRNA Transfer RNA (abbreviated tRNA and formerly referred to as sRNA, for soluble RNA) is an adaptor molecule composed of RNA, typically 76 to 90 nucleotides in length (in eukaryotes), that serves as the physical link between the mRNA and the amino ...
(also tRNA-like) splicing is another rare form of splicing that usually occurs in tRNA. The splicing reaction involves a different biochemistry than the spliceosomal and self-splicing pathways. In the
yeast Yeasts are eukaryotic, single-celled microorganisms classified as members of the fungus kingdom. The first yeast originated hundreds of millions of years ago, and at least 1,500 species are currently recognized. They are estimated to constit ...
''
Saccharomyces cerevisiae ''Saccharomyces cerevisiae'' () (brewer's yeast or baker's yeast) is a species of yeast (single-celled fungus microorganisms). The species has been instrumental in winemaking, baking, and brewing since ancient times. It is believed to have b ...
'', a yeast tRNA splicing
endonuclease Endonucleases are enzymes that cleave the phosphodiester bond within a polynucleotide chain. Some, such as deoxyribonuclease I, cut DNA relatively nonspecifically (without regard to sequence), while many, typically called restriction endonuclease ...
heterotetramer, composed of
TSEN54 TRNA splicing endonuclease subunit 54 is a protein that in humans is encoded by the TSEN54 gene. Function This gene encodes a subunit of the tRNA splicing endonuclease complex, which catalyzes the removal of introns from precursor tRNAs. The c ...
,
TSEN2 tRNA-splicing endonuclease subunit Sen2 is an enzyme that in humans is encoded by the ''TSEN2'' gene. tRNA splicing is a fundamental process required for cell growth and division. SEN2 is a subunit of the tRNA splicing endonuclease, which catalyz ...
,
TSEN34 tRNA-splicing endonuclease subunit Sen34 is an enzyme that in humans is encoded by the ''TSEN34'' gene. tRNA splicing is a fundamental process required for cell growth and division. SEN34 is a subunit of the tRNA splicing endonuclease, which cata ...
, and TSEN15, cleaves pre-tRNA at two sites in the acceptor loop to form a 5'-half tRNA, terminating at a 2',3'-cyclic phosphodiester group, and a 3'-half tRNA, terminating at a 5'-hydroxyl group, along with a discarded intron. Yeast tRNA kinase then phosphorylates the 5'-hydroxyl group using
adenosine triphosphate Adenosine triphosphate (ATP) is an organic compound that provides energy to drive many processes in living cells, such as muscle contraction, nerve impulse propagation, condensate dissolution, and chemical synthesis. Found in all known forms ...
. Yeast tRNA cyclic phosphodiesterase cleaves the cyclic phosphodiester group to form a 2'-phosphorylated 3' end. Yeast tRNA ligase adds an
adenosine monophosphate Adenosine monophosphate (AMP), also known as 5'-adenylic acid, is a nucleotide. AMP consists of a phosphate group, the sugar ribose, and the nucleobase adenine; it is an ester of phosphoric acid and the nucleoside adenosine. As a substit ...
group to the 5' end of the 3'-half and joins the two halves together. NAD-dependent 2'-phosphotransferase then removes the 2'-phosphate group.


Evolution

Splicing occurs in all the kingdoms or
domain Domain may refer to: Mathematics *Domain of a function, the set of input values for which the (total) function is defined ** Domain of definition of a partial function ** Natural domain of a partial function **Domain of holomorphy of a function * ...
s of life, however, the extent and types of splicing can be very different between the major divisions.
Eukaryote Eukaryotes () are organisms whose cells have a nucleus. All animals, plants, fungi, and many unicellular organisms, are Eukaryotes. They belong to the group of organisms Eukaryota or Eukarya, which is one of the three domains of life. Bacter ...
s splice many protein-coding
messenger RNA In molecular biology, messenger ribonucleic acid (mRNA) is a single-stranded molecule of RNA that corresponds to the genetic sequence of a gene, and is read by a ribosome in the process of synthesizing a protein. mRNA is created during the ...
s and some
non-coding RNA A non-coding RNA (ncRNA) is a functional RNA molecule that is not Translation (genetics), translated into a protein. The DNA sequence from which a functional non-coding RNA is transcribed is often called an RNA gene. Abundant and functionally im ...
s.
Prokaryote A prokaryote () is a single-celled organism that lacks a nucleus and other membrane-bound organelles. The word ''prokaryote'' comes from the Greek πρό (, 'before') and κάρυον (, 'nut' or 'kernel').Campbell, N. "Biology:Concepts & Con ...
s, on the other hand, splice rarely and mostly non-coding RNAs. Another important difference between these two groups of organisms is that prokaryotes completely lack the spliceosomal pathway. Because spliceosomal introns are not conserved in all species, there is debate concerning when spliceosomal splicing evolved. Two models have been proposed: the intron late and intron early models (see intron evolution).


Biochemical mechanism

Spliceosomal splicing and self-splicing involve a two-step biochemical process. Both steps involve
transesterification In organic chemistry, transesterification is the process of exchanging the organic group R″ of an ester with the organic group R' of an alcohol. These reactions are often catalyzed by the addition of an acid or base catalyst. The reaction ca ...
reactions that occur between RNA nucleotides. tRNA splicing, however, is an exception and does not occur by transesterification. Spliceosomal and self-splicing transesterification reactions occur via two sequential transesterification reactions. First, the 2'OH of a specific ''branchpoint'' nucleotide within the intron, defined during spliceosome assembly, performs a nucleophilic attack on the first nucleotide of the intron at the 5' splice site, forming the ''lariat intermediate''. Second, the 3'OH of the released 5' exon then performs an nucleophilic attack at the first nucleotide following the last nucleotide of the intron at the 3' splice site, thus joining the exons and releasing the intron lariat.


Alternative splicing

In many cases, the splicing process can create a range of unique proteins by varying the exon composition of the same mRNA. This phenomenon is then called
alternative splicing Alternative splicing, or alternative RNA splicing, or differential splicing, is an alternative splicing process during gene expression that allows a single gene to code for multiple proteins. In this process, particular exons of a gene may be i ...
. Alternative splicing can occur in many ways. Exons can be extended or skipped, or introns can be retained. It is estimated that 95% of transcripts from multiexon genes undergo alternative splicing, some instances of which occur in a tissue-specific manner and/or under specific cellular conditions. Development of high throughput mRNA sequencing technology can help quantify the expression levels of alternatively spliced isoforms. Differential expression levels across tissues and cell lineages allowed computational approaches to be developed to predict the functions of these isoforms. Given this complexity, alternative splicing of pre-mRNA transcripts is regulated by a system of trans-acting proteins (activators and repressors) that bind to cis-acting sites or "elements" (enhancers and silencers) on the pre-mRNA transcript itself. These proteins and their respective binding elements promote or reduce the usage of a particular splice site. The binding specificity comes from the sequence and structure of the cis-elements, e.g. in HIV-1 there are many donor and acceptor splice sites. Among the various splice sites, ssA7, which is 3' acceptor site, folds into three stem loop structures, i.e. Intronic splicing silencer (ISS), Exonic splicing enhancer (ESE), and Exonic splicing silencer (ESSE3). Solution structure of Intronic splicing silencer and its interaction to host protein hnRNPA1 give insight into specific recognition. However, adding to the complexity of alternative splicing, it is noted that the effects of regulatory factors are many times position-dependent. For example, a splicing factor that serves as a splicing activator when bound to an intronic enhancer element may serve as a repressor when bound to its splicing element in the context of an exon, and vice versa. In addition to the position-dependent effects of enhancer and silencer elements, the location of the branchpoint (i.e., distance upstream of the nearest 3’ acceptor site) also affects splicing. The secondary structure of the pre-mRNA transcript also plays a role in regulating splicing, such as by bringing together splicing elements or by masking a sequence that would otherwise serve as a binding element for a splicing factor.


Role of splicing/alternative splicing in HIV-integration

The process of splicing is linked with
HIV integration AIDS ("acquired immune deficiency syndrome") is caused by the human immunodeficiency virus (HIV). Individuals with HIV have what is referred to as a "HIV infection". When infected semen, vagina, vaginal secretions, or blood come in contact with the ...
, as HIV-1 targets highly spliced genes.


Splicing response to DNA damage

DNA damage DNA repair is a collection of processes by which a cell identifies and corrects damage to the DNA molecules that encode its genome. In human cells, both normal metabolic activities and environmental factors such as radiation can cause DNA d ...
affects splicing factors by altering their
post-translational modification Post-translational modification (PTM) is the covalent and generally enzymatic modification of proteins following protein biosynthesis. This process occurs in the endoplasmic reticulum and the golgi apparatus. Proteins are synthesized by ribo ...
, localization, expression and activity. Furthermore, DNA damage often disrupts splicing by interfering with its coupling to transcription. DNA damage also has an impact on the splicing and alternative splicing of genes intimately associated with
DNA repair DNA repair is a collection of processes by which a cell identifies and corrects damage to the DNA molecules that encode its genome. In human cells, both normal metabolic activities and environmental factors such as radiation can cause DNA d ...
. For instance, DNA damages modulate the alternative splicing of the DNA repair genes ''
Brca1 Breast cancer type 1 susceptibility protein is a protein that in humans is encoded by the ''BRCA1'' () gene. Orthologs are common in other vertebrate species, whereas invertebrate genomes may encode a more distantly related gene. ''BRCA1'' is a ...
'' and '' Ercc1''.


Experimental manipulation of splicing

Splicing events can be experimentally altered by binding steric-blocking antisense oligos, such as
Morpholino A Morpholino, also known as a Morpholino oligomer and as a phosphorodiamidate Morpholino oligomer (PMO), is a type of oligomer molecule (colloquially, an oligo) used in molecular biology to modify gene expression. Its molecular structure contain ...
s or
Peptide nucleic acid Peptide nucleic acid (PNA) is an artificially synthesized polymer similar to DNA or RNA. Synthetic peptide nucleic acid oligomers have been used in recent years in molecular biology procedures, diagnostic assays, and antisense therapies. Due to ...
s to snRNP binding sites, to the branchpoint nucleotide that closes the lariat, or to splice-regulatory element binding sites.


Splicing errors and variation

It has been suggested that one third of all disease-causing mutations impact on splicing. Common errors include: *Mutation of a splice site resulting in loss of function of that site. Results in exposure of a premature
stop codon In molecular biology (specifically protein biosynthesis), a stop codon (or termination codon) is a codon (nucleotide triplet within messenger RNA) that signals the termination of the translation process of the current protein. Most codons in mess ...
, loss of an exon, or inclusion of an intron. *Mutation of a splice site reducing specificity. May result in variation in the splice location, causing insertion or deletion of amino acids, or most likely, a disruption of the
reading frame In molecular biology, a reading frame is a way of dividing the sequence of nucleotides in a nucleic acid ( DNA or RNA) molecule into a set of consecutive, non-overlapping triplets. Where these triplets equate to amino acids or stop signals during ...
. *Displacement of a splice site, leading to inclusion or exclusion of more RNA than expected, resulting in longer or shorter exons. Although many splicing errors are safeguarded by a cellular quality control mechanism termed
nonsense-mediated mRNA decay Nonsense-mediated mRNA decay (NMD) is a surveillance pathway that exists in all eukaryotes. Its main function is to reduce errors in gene expression by eliminating mRNA transcripts that contain premature stop codons. Translation of these aberrant ...
(NMD), a number of splicing-related diseases also exist, as suggested above. Allelic differences in mRNA splicing are likely to be a common and important source of phenotypic diversity at the molecular level, in addition to their contribution to genetic disease susceptibility. Indeed, genome-wide studies in humans have identified a range of genes that are subject to allele-specific splicing. In plants, variation for flooding stress tolerance correlated with stress-induced alternative splicing of transcripts associated with gluconeogenesis and other processes.


Protein splicing

In addition to RNA, proteins can undergo splicing. Although the biomolecular mechanisms are different, the principle is the same: parts of the protein, called inteins instead of introns, are removed. The remaining parts, called exteins instead of exons, are fused together. Protein splicing has been observed in a wide range of organisms, including bacteria,
archaea Archaea ( ; singular archaeon ) is a domain of single-celled organisms. These microorganisms lack cell nuclei and are therefore prokaryotes. Archaea were initially classified as bacteria, receiving the name archaebacteria (in the Archaeba ...
, plants, yeast and humans.


See also

*
cDNA In genetics, complementary DNA (cDNA) is DNA synthesized from a single-stranded RNA (e.g., messenger RNA (mRNA) or microRNA (miRNA)) template in a reaction catalyzed by the enzyme reverse transcriptase. cDNA is often used to express a sp ...
* DBASS3/5 *
Exon junction complex An exon junction complex (EJC) is a protein complex which forms on a pre-messenger RNA strand at the junction of two exons which have been joined together during RNA splicing. The EJC has major influences on translation, surveillance and locali ...
* mRNA capping *
Polyadenylation Polyadenylation is the addition of a poly(A) tail to an RNA transcript, typically a messenger RNA (mRNA). The poly(A) tail consists of multiple adenosine monophosphates; in other words, it is a stretch of RNA that has only adenine bases. In euk ...
*
Post-transcriptional modification Transcriptional modification or co-transcriptional modification is a set of biological processes common to most eukaryotic cells by which an RNA primary transcript is chemically altered following transcription from a gene to produce a mature, ...
* RNA editing *
SWAP protein domain In molecular biology, the protein domain SWAP is derived from the term Suppressor-of-White-APricot, a splicing regulator from the model organism ''Drosophila melanogaster''. The protein domain is found in regulators that control splicing. It is fo ...
, a splicing regulator


References


External links


Virtual Cell Animation Collection: mRNA Splicing
* {{DEFAULTSORT:Rna Splicing Gene expression Spliceosome