RNA splicing
For many eukaryotic introns, splicing occurs in a series of reactions which are catalyzed by the spliceosome, a complex of small nuclear ribonucleoproteins (snRNPs).
The process of transcription, splicing and translation is called gene expression, the central dogma of molecular biology.
The word intron is derived from the terms intragenic region,[1] and intracistron,[2] that is, a segment of DNA that is located between two exons of a gene.
The splice donor site includes an almost invariant sequence GU at the 5' end of the intron, within a larger, less highly conserved region.
Further upstream from the polypyrimidine tract is the branchpoint, which includes an adenine nucleotide involved in lariat formation.
In this way, a point mutation, which might otherwise affect only a single amino acid, can manifest as a deletion or truncation in the final protein.
[citation needed] Splicing is catalyzed by the spliceosome, a large RNA-protein complex composed of five small nuclear ribonucleoproteins (snRNPs).
[20] Self-splicing occurs for rare introns that form a ribozyme, performing the functions of the spliceosome by RNA alone.
Yeast tRNA ligase adds an adenosine monophosphate group to the 5' end of the 3'-half and joins the two halves together.
[26] In many cases, the splicing process can create a range of unique proteins by varying the exon composition of the same mRNA.
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.
[27] 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.
Solution structure of Intronic splicing silencer and its interaction to host protein hnRNPA1 give insight into specific recognition.
[31] 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.
[35] DNA damage affects splicing factors by altering their post-translational modification, localization, expression and activity.
[44] 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.
In plants, variation for flooding stress tolerance correlated with stress-induced alternative splicing of transcripts associated with gluconeogenesis and other processes.
Although the biomolecular mechanisms are different, the principle is the same: parts of the protein, called inteins instead of introns, are removed.
Protein splicing has been observed in a wide range of organisms, including bacteria, archaea, plants, yeast and humans.
