MBB331_Week10-Fall-2011

5 gpppapnp pp p ppapnp pp 5 5 5 5 56 weaver

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Unformatted text preview: ence for developmental evidence importance of methylation: 5importance azacytidine incorporated into DNA, in azacytidine place of cytidine, cannot be methylated & causes inappropriate induction of developmental genes, and activates the silent X chromosome chromosome 54 Lewin Genes VI 1999 Oxford University Press EUKARYOTIC MODIFICATION OF RNA: OVERVIEW OVERVIEW Primary eukaryotic transcript: pre-mRNA, Primary same organization as the gene same -pre-mRNA processing: (1) add’n of 5´ end cap (2) 3´ end polyadenylation (3) Intron splicing Lewin Genes VII 2000 Oxford University Press 55 CAP STRUCTURES CAP STRUCTURES AT 5´ mRNA ENDS nuclear -nuclear transcripts usually begin with purines (5´pppA or 5´pppG) purines -5´ends capped with terminal G by guanylyl -5´ends transferase (immediately after transcription) transferase -terminal G attached in reverse orientation -terminal by 5´-5´ triphosphate link: by Gppp 5´+ 5´pppApNp... 5´+ -->GpppApNp… + pp + p --> ppApNp… pp 5´-5´ 5´-5´ 56 Weaver 2002 Molecular Biology Ed. 2 CAP STRUCTURES CAP STRUCTURES AT 5´ mRNA ENDS -cap is substrate for several methylation -cap events: events: -in all eukaryotes, meth. at 7 position; a cap -in possessing this single group is cap 0 cap -in all but unicellular euk. a methyl is added -in to the 2´-O (ribose) position of second base (originally 1st base of transcript); this is cap 1 cap -in some cases in higher euk. another -in methyl is added to second base, if adenin...
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