GEN409Presentation 6

GEN409Presentation 6 - Presentation 6 "Chapter 21 ! RNA...

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1 RNA Splicing and Processing The 5’ End of Eukaryotic mRNA is capped Nuclear splice junctions are short sequences Splice junctions are read in pairs Pre-mRNA splicing proceeds through a lariat snRNAs are required for splicing Commitment of pre-mRNA to the splicing pathway Presentation 6 Chapter 21
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2 unprocessed mRNA = pre mRNA – primary transcript has the same organization of the DNA exists in the nucleus as an RNA particle After processing: mature mRNA is transported through nuclear pores into the cytoplasm for translation. Figure 21.1 *
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pre-mRNA –The nuclear transcript that is processed by modifcation and splicing to give an mRNA. RNA splicing – The process oF excising introns From RNA and connecting the exons into a continuous mRNA. o Splice sites are the sequences immediately surrounding the exon–intron boundaries. o They are named For their positions relative to the intron. o The 5 ! splice site at the 5 ! (leFt) end oF the intron includes the consensus sequence GU. o The 3 ! splice site at the 3 ! (right) end oF the intron includes the consensus sequence AG. heterogeneous nuclear RNA (hnRNA) – RNA that comprises transcripts oF nuclear genes made by RNA polymerase II; it has a wide size distribution and low stability. hnRNP – The ribonucleoprotein Form oF hnRNA (heterogeneous nuclear RNA), in which the hnRNA is complexed with proteins. o Pre-mRNAs are not exported until processing is complete; thus they are Found only in the nucleus. small cytoplasmic RNAs (scRNA; scyrps) – RNAs that are present in the cytoplasm (and sometimes are also Found in the nucleus). small nuclear RNA (snRNA; snurps) – One oF many small RNA species confned to the nucleus; several oF them are involved in splicing or other RNA processing reactions. small nucleolar RNA (snoRNA) – A small nuclear RNA that is localized in the nucleolus. HelpFul Defnitions:
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4 Figure 21.2 The 5 ! End of Eukaryotic mRNA Is Capped A 5 ! cap is formed by adding a G to the terminal base of the transcript via a 5 ! –5 ! link. The capping process takes place during the transcription, which may be important for transcription reinitiation. The 5 ! cap of most mRNA is monomethylated, but some small noncoding RNAs are trimethylated. The cap structure is recognized by protein factors to in±uence mRNA stability, splicing, export, and translation. In the nucleus, the cap is recognized and bound by the cap binding CBP20/80 complex. It stimulates splicing of the ²rst intron. It directly interacts with the mRNA
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This note was uploaded on 09/25/2011 for the course GEN 409 taught by Professor Linda during the Spring '09 term at Iowa State.

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GEN409Presentation 6 - Presentation 6 "Chapter 21 ! RNA...

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