Prp8: Difference between revisions

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==Pre-mRNA Splicing==

Pre-mRNA splicing is carried out by one of the most complex pieces of cellular machinery known to date; the Spliceosome. It is a large, catalytic protein-RNA complex responsible for removing the intronic sequences of pre-mRNA and “splicing” together the exonic sequences to form mature mRNA. The spliceosome is made up of approximately 145 distinct spliceosomal proteins, and five small nuclear RNAs (snRNAs) <ref name='Comprehensive proteomic analysis of the human spliceosome'>DOI:10.1038/nature01031</ref>. The five snRNAs have been subsequently named U1, U2, U4, U5, and U6. The spliceosome carries out a two-step transesterification reaction through a series of chemical steps in order to remove the intronic sequences from the pre-mRNA, which is facilitated by the movements, rearrangements, and dynamic exchanges of the snRNAs and splicing associated proteins <ref name='Messenger RNA Splicing in Yeast: Clues to Why the Spliceosome is a Ribonucleoprotein'>PMID:1853200</ref>.

[[Image:Spliceosome.jpg]]

Pre-mRNA splicing is carried out by one of the most complex pieces of cellular machinery known to date; the Spliceosome. It is a large, catalytic protein-RNA complex responsible for removing the intronic sequences of pre-mRNA and “splicing” together the exonic sequences to form mature mRNA. The spliceosome is made up of approximately 145 distinct spliceosomal proteins, and five small nuclear RNAs (snRNAs) <ref name='Comprehensive proteomic analysis of the human spliceosome'>DOI:10.1038/nature01031</ref>. The five snRNAs have been subsequently named U1, U2, U4, U5, and U6. The spliceosome carries out a two-step transesterification reaction through a series of chemical steps in order to remove the intronic sequences from the pre-mRNA, which is facilitated by the movements, rearrangements, and dynamic exchanges of the snRNAs and splicing associated proteins <ref name='Messenger RNA Splicing in Yeast: Clues to Why the Spliceosome is a Ribonucleoprotein'>PMID:1853200</ref>.

First, the U1 snRNP recognizes and binds to the 5’ splice site of the pre-mRNA and the U2 snRNP recognizes and binds to the branch site of the intronic sequence, which contains a conserved adenine nucleotide, which is collectively known as complex A <ref name='Biochemical Mechanisms of Constitutive and Regulated PRE-mRNA Splicing'>DOI:10.1146/annurev.cb.07.110191.003015</ref>. Subsequently, the U4/U6 U5 tri-snRNP moves in and associates with the intronic sequence (now known as complex B)<ref name='Biochemical Mechanisms of Constitutive and Regulated PRE-mRNA Splicing'/>. This causes the U4 and U1 snRNPs to be displaced, forming the catalytically active spliceosome (complex B*) and the remaining U2, U5, and U6 snRNP facilitate the two transesterification reactions, dissociate from the now mature mRNA, and are recycled for subsequent use in another splicing reaction <ref name='Biochemical Mechanisms of Constitutive and Regulated PRE-mRNA Splicing'/>.

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 ==Pre-mRNA Splicing==
+Pre-mRNA splicing is carried out by one of the most complex pieces of cellular machinery known to date; the Spliceosome. It is a large, catalytic protein-RNA complex responsible for removing the intronic sequences of pre-mRNA and “splicing” together the exonic sequences to form mature mRNA. The spliceosome is made up of approximately 145 distinct spliceosomal proteins, and five small nuclear RNAs (snRNAs) <ref name='Comprehensive proteomic analysis of the human spliceosome'>DOI:10.1038/nature01031</ref>. The five snRNAs have been subsequently named U1, U2, U4, U5, and U6. The spliceosome carries out a two-step transesterification reaction through a series of chemical steps in order to remove the intronic sequences from the pre-mRNA, which is facilitated by the movements, rearrangements, and dynamic exchanges of the snRNAs and splicing associated proteins <ref name='Messenger RNA Splicing in Yeast: Clues to Why the Spliceosome is a Ribonucleoprotein'>PMID:1853200</ref>.
 [[Image:Spliceosome.jpg]]
-Pre-mRNA splicing is carried out by one of the most complex pieces of cellular machinery known to date; the Spliceosome. It is a large, catalytic protein-RNA complex responsible for removing the intronic sequences of pre-mRNA and “splicing” together the exonic sequences to form mature mRNA. The spliceosome is made up of approximately 145 distinct spliceosomal proteins, and five small nuclear RNAs (snRNAs) <ref name='Comprehensive proteomic analysis of the human spliceosome'>DOI:10.1038/nature01031</ref>. The five snRNAs have been subsequently named U1, U2, U4, U5, and U6. The spliceosome carries out a two-step transesterification reaction through a series of chemical steps in order to remove the intronic sequences from the pre-mRNA, which is facilitated by the movements, rearrangements, and dynamic exchanges of the snRNAs and splicing associated proteins <ref name='Messenger RNA Splicing in Yeast: Clues to Why the Spliceosome is a Ribonucleoprotein'>PMID:1853200</ref>.
 First, the U1 snRNP recognizes and binds to the 5’ splice site of the pre-mRNA and the U2 snRNP recognizes and binds to the branch site of the intronic sequence, which contains a conserved adenine nucleotide, which is collectively known as complex A <ref name='Biochemical Mechanisms of Constitutive and Regulated PRE-mRNA Splicing'>DOI:10.1146/annurev.cb.07.110191.003015</ref>. Subsequently, the U4/U6 U5 tri-snRNP moves in and associates with the intronic sequence (now known as complex B)<ref name='Biochemical Mechanisms of Constitutive and Regulated PRE-mRNA Splicing'/>. This causes the U4 and U1 snRNPs to be displaced, forming the catalytically active spliceosome (complex B*) and the remaining U2, U5, and U6 snRNP facilitate the two transesterification reactions, dissociate from the now mature mRNA, and are recycled for subsequent use in another splicing reaction <ref name='Biochemical Mechanisms of Constitutive and Regulated PRE-mRNA Splicing'/>.