Splicing - Post-transcriptional Processing of mRNA in...

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Post-transcriptional Processing of mRNA in Eukaryotes Translation closely follows transcription in prokaryotes In eukaryotes, these processes are separated - transcription in nucleus, translation in cytoplasm On the way from nucleus to cytoplasm, the mRNA is converted from "primary transcript" to "mature mRNA"
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Exons and introns Both vary in size In general, human introns are larger Splicing is complex and precise RNA processing also includes capping, methylation and poly A tail addition Also called pre-mRNA
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Capping Primary transcripts are usually first "capped" by a guanylyl group The reaction is catalyzed by guanylyl transferase which transfers guanly from GTP to 5’end of transcript (already has 5’ PPP) Pp is liberated from GTP; and terminal p from transcript Gppp + pppApNpNpNp…. GpppApNpNpNp…
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Methylation of Cap N7 position of G cap gets methylated (7MeGppp Cap) 2’ O position of 2nd and 3rd nucleotides can also methylated First A residue usualy has methylation at 2’O Variations also occur:
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What is the function of the Cap? Protection from degradation: Capped mRNAs are degraded much more slowly than non-capped mRNAs, due to the fact that the 5' to 5' link of the cap blocks the action of RNases that degrade mRNA from the 5' end of an RNA molecule. Increased translatability: stimulates translation of mRNA about 300-fold Transport from nucleus to the cytoplasm
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3'-Polyadenylylation to create Poly A Tail Termination of transcription occurs only after RNA polymerase has transcribed past a consensus AAUAAA sequence - the poly(A)+ addition site
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This note was uploaded on 03/31/2008 for the course BCHM 4115 taught by Professor Emgregory during the Spring '08 term at Virginia Tech.

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Splicing - Post-transcriptional Processing of mRNA in...

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