2 sharp 1977 eukaryotic genes are sharp interrupted

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Unformatted text preview: s associated with PABP mRNA after other proteins have dissociated have polyAs polyAs Phase 2: PABP Phase promotes polyA tail extension to ~200 A’s extension 62 mRNA: WHY HAVE A TAIL? mRNA: WHY HAVE A TAIL? • Why have a polyadenylated tail? – May contribute to mRNA stability by its May continued association with PABP (polyA binding protein) after the other proteins dissociate proteins – May contribute to translational initiation – May be required for intron splicing May nearest to 3´ end nearest 63 Histone mRNA: Some eukaryotic mRNAs not polyadenylated mRNAs • Discrete 3´ends of histone Discrete mRNA depend on RNA structure - histone mRNA terminates in a stem-loop terminates – Cleavage of histone mRNA Cleavage at correct position requires , in addition to hairpin, U7 a small nuclear (sn)RNA whose 5´end is complementary to seq downstream of 3´cleavage site of mRNA site – U7 snRNA therefore U7 functions in ribonucleoprotein complex in mRNA cleavage cleavage Lewin Genes VII 2000 Oxford University Press 64 (1) pre­mRNA SPLICING: R­LOOPING Weaver 2002 Molecular Biology Ed. 2 • Sharp (1977): eukaryotic genes are Sharp interrupted interrupted • Observed by R-looping: RNA Observed R-looping RNA hybridized to DNA template & viewed by EM microscopy viewed • Adenovirus hexon gene: DNA loops Adenovirus observed indicating DNA sequences not completely paired with mRNA ie. DNA seq not ie DNA represented in mRNA represented • Further evidence for existe...
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