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Lecture 28 - RNA Processing - BIOL308.pdf

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BIOL 308
Bruce Wolff

Lecture 28RNA ProcessingPosttranscriptional control after transcription by RNAPIISplicing of primary transcriptsProcessing of mRNA SplicingInitially seen using electron microscopy 1977Rlooping techniqueSplice sites can be determined by comparing genomic DNA with cDNA or mRNAHybridization between globin precursor RNA and globin geneOvalbumin DNA hybridized with mRNA 7 distinct loopsThe Origin of introns is not clearA few bacteria and archaebacteria and organelles of some organisms have some intronsYeastfew introns and well conserved splice and branch site sequencesHigher organismsoften multiple introns within a single premRNA poorly defined splice and branch site sequences regulatory system controlling their selection is necessaryHypothesisrolesMaybe represent sites of recombination between ancient minigenes the exonsIntron RNA involved in some processes needed for specific functionssnoRNA small antisense RNAs etcEfficiencydifferent protein products from a single gene using alternative splicingIntrons are 410 times the length of exons in average Average human gene 78 intronsA few genes have no introns eg Histone genes interferon geneSplicing may be constitutive same introns are always identified and spliced out single protein productHigher organisms alternative splicingSame premRNA is spliced in different ways in different tissues or different developmentaldifferentiation stages to generate functionally different isoforms of a proteinMore rarely transsplicingcan also generate unique mRNAs by association andlinking of exons from different premRNAThe Mechanism for SplicingGroup I and II intronsselfsplicingintronsRNA is splicing itself NO proteins involved RNAribozymeSpecific nucleotides at 5 and 3 edgesintron5 and 3 splice sitesMutation single base substitution accumulation of unspliced precursorsThe above sequence is present in almost all premRNAs which will undergospliceosomal splicingGroup II intronsremoved as a lariat structure in two transesterification reaction NOTES FROM LECTURES Page 1
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