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Alternative splicing, alternative RNA splicing, or differential splicing, is an alternative splicing process during gene expression that allows a single gene to produce different splice variants. For example, some exons of a gene may be included within or excluded from the final RNA product of the gene. [ 1 ]
Alternative splicing is regulated so that each mature mRNA may encode a multiplicity of proteins. Alternative splicing of the primary transcript. The effect of alternative splicing in gene expression can be seen in complex eukaryotes which have a fixed number of genes in their genome yet produce much larger numbers of different gene products. [9]
RNA splicing is a process in molecular biology where a newly-made precursor messenger RNA (pre-mRNA) transcript is transformed into a mature messenger RNA ().It works by removing all the introns (non-coding regions of RNA) and splicing back together exons (coding regions).
The pre-mRNA processing at the 3' end of the RNA molecule involves cleavage of its 3' end and then the addition of about 250 adenine residues to form a poly(A) tail.The cleavage and adenylation reactions occur primarily if a polyadenylation signal sequence (5'- AAUAAA-3') is located near the 3' end of the pre-mRNA molecule, which is followed by another sequence, which is usually (5'-CA-3') and ...
These include the 5' end splice site, the branch point sequence, the polypyrimidine tract, and the 3' end splice site. The spliceosome catalyzes the removal of introns, and the ligation of the flanking exons. [citation needed] Introns typically have a GU nucleotide sequence at the 5' end splice site, and an AG at the 3' end splice site.
Where intron-generating transposons do not create target site duplications, elements include both splice sites GT (5') and AG (3') thereby splicing precisely without affecting the protein-coding sequence. [65] It is not yet understood why these elements are spliced, whether by chance, or by some preferential action by the transposon.
In protein-coding genes, the exons include both the protein-coding sequence and the 5′- and 3′-untranslated regions (UTR). Often the first exon includes both the 5′-UTR and the first part of the coding sequence, but exons containing only regions of 5′-UTR or (more rarely) 3′-UTR occur in some genes, i.e. the UTRs may contain introns. [11]
The spliceosome, [5] a protein-RNA complex located in the nucleus, catalyzes splicing in the following manner: The spliceosome recognizes an intron, which is flanked by specific sequences at its 5' and 3' ends, known as a donor splice site (or 5' splice site) and an acceptor splice site (or 3' splice site), respectively.