Mechanism of Splicing

The binding of snRNP brings the sequences of the neighboring exons into the correct alignment for splicing
Splicing occurs in several steps and is catalyzed by small nuclear ribonucleoproteins (snRNPs, commonly pronounced “snurps”).
It start with a cut in the 5′ splice donor site.

Introns are removed from primary transcripts by cleavage at conserved sequences called splice sites. These sites are found at the 5′ and 3′ ends of introns.
The cut end then attaches to the conserved branch point region downstream through pairing of guanine and adenine nucleotides from the 5′ end and the branch point to form a looped structure known as a lariat
The bonding of the guanine and adenine bases takes place via a chemical reaction known as transesterification
The guanine residue (introns) is thus cleaved from the RNA strand and forms a new bond with the adenine.
an OH group at the 3′ end of the exon attacks the phosphodiester bond at the 3′ splice site.
The adjoining exons are covalently bound, and the resulting lariat is released with U2, U5, and U6 bound to it.
After introns have been removed and exons joined, the mature mRNA molecules leave the nucleus and pass into the cytosol through pores in the nuclear membrane.
Self Splicing :Certain hnRNA itself has splicing activity Because of Ribozyme activity.
mutations that cause the incorrect splicing of p-globin mRNA are responsible for some cases of β-thalassemia.
Selective Splicing- selective inclusion or exclusion of exons
Altemative 5’donor site- S’ donor site of certain exons is changed.
Alternative 3′ acceptor site- 3′ acceptor site of certain exons is changed.
Alternative Polyadenylation site-Different site is used for Poly-adenylation.

Introns are removed from primary transcripts by cleavage at conserved sequences called splice sites. These sites are found at the 5′ and 3′ ends of introns.
The cut end then attaches to the conserved branch point region downstream through pairing of guanine and adenine nucleotides from the 5′ end and the branch point to form a looped structure known as a lariat
The bonding of the guanine and adenine bases takes place via a chemical reaction known as transesterification
The guanine residue (introns) is thus cleaved from the RNA strand and forms a new bond with the adenine.
an OH group at the 3′ end of the exon attacks the phosphodiester bond at the 3′ splice site.
The adjoining exons are covalently bound, and the resulting lariat is released with U2, U5, and U6 bound to it.
After introns have been removed and exons joined, the mature mRNA molecules leave the nucleus and pass into the cytosol through pores in the nuclear membrane.
Self Splicing :Certain hnRNA itself has splicing activity Because of Ribozyme activity.
mutations that cause the incorrect splicing of p-globin mRNA are responsible for some cases of β-thalassemia.
Selective Splicing- selective inclusion or exclusion of exons
Altemative 5’donor site- S’ donor site of certain exons is changed.
Alternative 3′ acceptor site- 3′ acceptor site of certain exons is changed.
Alternative Polyadenylation site-Different site is used for Poly-adenylation

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