Prp24: Difference between revisions
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== Introduction == | == Introduction == | ||
[[Image:Spliceosome.jpg |frame|left| Figure 1. Assembly and disassembly of the spliceosome in ''Saccharomyces cerevisiae'' (after Staley and Guthrie 1998 <ref name="Staley"/>)]] | |||
[[Image:Transester.jpg |frame|left| Figure 2. The transesterificiation reactions of pre-mRNA splicing (after Brow 2002<ref name="Brow review"/>) ]] | |||
=== Pre-mRNA Splicing === | |||
Pre-mRNA splicing is an essential process in eukaryotes that removes non-coding introns from a pre-mRNA transcript and splices coding exons together before the mRNA is exported from the nucleus for translation into a protein<ref name="Staley">PMID:9476892</ref>. Splicing requires five snRNPs (U1, U2, U4, U5, U6), several other proteins, and the input of energy from ATP. The U1 and U2 snRNPs assemble individually on the pre-mRNA transcript, while U4 and U6 form a U4/U6 di-snRNP before interacting with U5 to form a U4/U6.U5 tri-snRNP that combines with U1 and U2 at the pre-mRNA transcript (Fig 1)<ref name="Staley"/>. U4 and U1 then depart, and after conformational changes and base pair formation with the pre-mRNA the remaining snRNPs form the catalytically active spliceosome<ref name="Staley"/>. Two transesterification reactions then occur; the first reaction is the nucleophillic attack of the phosphate group at the end of the 5' exon by the 2' hydroxyl of a specific adenosine at the branch point sequence of the intron (Fig 2)<ref name="Brow review">PMID:12429696</ref>. This is then followed by the nucleophillic attack of the phosphate group linking the 3' exon to the intron by the 3' hydroxyl of the 5' exon<ref name="Brow review"/>. These splicing reactions, as well as the addition of 7-methylguanosine 5' cap and a 3' polyadenosine tail, results in a mature mRNA transcript that can be exported from the nucleus and translated into a protein. | Pre-mRNA splicing is an essential process in eukaryotes that removes non-coding introns from a pre-mRNA transcript and splices coding exons together before the mRNA is exported from the nucleus for translation into a protein<ref name="Staley">PMID:9476892</ref>. Splicing requires five snRNPs (U1, U2, U4, U5, U6), several other proteins, and the input of energy from ATP. The U1 and U2 snRNPs assemble individually on the pre-mRNA transcript, while U4 and U6 form a U4/U6 di-snRNP before interacting with U5 to form a U4/U6.U5 tri-snRNP that combines with U1 and U2 at the pre-mRNA transcript (Fig 1)<ref name="Staley"/>. U4 and U1 then depart, and after conformational changes and base pair formation with the pre-mRNA the remaining snRNPs form the catalytically active spliceosome<ref name="Staley"/>. Two transesterification reactions then occur; the first reaction is the nucleophillic attack of the phosphate group at the end of the 5' exon by the 2' hydroxyl of a specific adenosine at the branch point sequence of the intron (Fig 2)<ref name="Brow review">PMID:12429696</ref>. This is then followed by the nucleophillic attack of the phosphate group linking the 3' exon to the intron by the 3' hydroxyl of the 5' exon<ref name="Brow review"/>. These splicing reactions, as well as the addition of 7-methylguanosine 5' cap and a 3' polyadenosine tail, results in a mature mRNA transcript that can be exported from the nucleus and translated into a protein. | ||
