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Exon shuffling is a molecular mechanism for the formation of new genes. It is a process through which two or more exons from different genes can be brought together ectopically , or the same exon can be duplicated , to create a new exon-intron structure. [ 1 ]
Across all eukaryotic genes in GenBank, there were (in 2002), on average, 5.48 exons per protein coding gene. The average exon encoded 30-36 amino acids. [7] While the longest exon in the human genome is 11555 bp long, several exons have been found to be only 2 bp long. [8] A single-nucleotide exon has been reported from the Arabidopsis genome. [9]
The free 5' exon then attacks the 3' splice site, joining the two exons and releasing a structure known as an intron lariat. The intron lariat is subsequently de-branched and quickly degraded. [5] Pre-mRNA to mRNA splicing
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. [1] The term intron refers to both the DNA sequence within a gene and the corresponding RNA sequence in RNA transcripts. [2]
During the process of splicing, an RNA-protein catalytical complex known as spliceosome catalyzes two transesterification reactions, which remove an intron and release it in form of lariat structure, and then splice neighbouring exons together. [11] In certain cases, some introns or exons can be either removed or retained in mature mRNA. [12]
Multiple short probes matching a single transcript can reveal details about the intron-exon structure, requiring statistical models to determine the authenticity of the resulting signal. RNA-Seq studies produce billions of short DNA sequences, which must be aligned to reference genomes composed of millions to billions of base pairs.
The genomic fragment is inserted into the intron of a 'splicing vector' consisting of a known exon - intron - exon sequence of DNA, and the vector is then inserted into an eukaryotic cell. If the fragment does not contain exons (i.e., consists solely of intron DNA), it will be spliced out together with the vector's original intron.
Splicing of group I introns is processed by two sequential transesterification reactions. [3] First an exogenous guanosine or guanosine nucleotide (exoG) docks onto the active G-binding site located in P7, and then its 3'-OH is aligned to attack the phosphodiester bond at the "upstream" (closer to the 5' end) splice site located in P1, resulting in a free 3'-OH group at the upstream exon and ...