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2000 molecular cell biology 40 ed wh freeman and co

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Unformatted text preview: rylated in CTD (RNAP IIO) carries out transcript elongation -in in vitro splicing assays IIO aids splicing of pre-mRNAs whereas RNAP IIA (unphos. RNA Pol II) inhibits splicing 13 Other contributors to splicing Lodish et al. 2000. Molecular Cell Biology 4.0. Ed. W.H. Freeman and Co Lodish et 14 15 -effects on splicing occur at level of spliceosome assembly -study indicates that while RNAP IIO is transcribing mRNA it is also helping to set up spliceosomes -why does RNAP IIA inhibit splicing? -RNAP IIA can transcribe certain intronless genesability to suppress splicing may prevent accidental 16 splicing of such transcripts -this study, and others mentioned in Weaver, have led to a model for participation of RNA polymerase CTD in splicing by assisting in assembly of splicing factors 17 (2) SELF­SPLICING INTRONS (2) SELF­SPLICING INTRONS • Thomas Cech (1980s): 26S rRNA of Thomas ciliated protozoan Tetrahymena catalyzes splicing of its own (group I) intron without the requirement of a protein without • Group I introns spliced out by Group “conventional” 2 transesterifications “conventional” • Mitochondrial group II introns: also selfsplicing & mechanistically similar to splicing spliceosome splicing spliceosome 18 SPLICING ACTIVE CENTERS: SPLICEOSOME vs. GROUP II INTRON SPLICEOSOME Weaver 2002 Molecular Biology Ed. 2 • spliceosome RNA structure poised for second spliceosome transesterification looks like group II introns at similar stage of splicing similar • Spliceosomal snRNPs substitute for catalytic Spliceosomal center of group II introns 19 WHY SPLICE? WHY SPLICE? • Introns of nuclear pre-mRNAs descended Introns from group II introns that cannot self-excise & dependent on trans-acting snRNAs with proteins proteins • snRNPs much more efficient than selfsplicing & reduces need for intron selfsplicing • Why are introns maintained? Exon shuffling Why Exon allows creation of new genes & alternate splicing permits regulated attachment of new functional domains to specific protein new 20 ALTERNATIVE SPLICING ALTERNATIVE Weaver 2002 Molecular Biology Ed. 2 • ~1 in 20 pre-mRNAs spliced in alternative ways giving 2 or ~1 more mRNAs encoding different proteins more • alternative splicing can have important biol...
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