T branch site deleted branch branch site targets the

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Unformatted text preview: f bands (>300 bands expected if 7 introns removed randomly) introns • Splicing occurs by specific order Splicing of events…. Intron 5 or 6 are the first removed, then the other is the second intron removed, intron 3 is never lost during one of the first 3 steps…. steps…. • The order of intron removal for The ovomucoid is: intron 5/6 ---> 7/4 ---> 2 ---> 3/1 ---> • But… other order pathways exist Lewin Genes VII 2000 Oxford University Press 70 NUCLEAR mRNA PRECURSOR SPLICING NUCLEAR mRNA PRECURSOR SPLICING • (1) Cut at 5´splice site (1) separating left exon from right intron-exon RNA intron-exon • (2) Right intron-exon forms (2) lariat linking 5´ end to 2´-OH lariat on target A within intron ---> 5 on ´-2´ branch site formed ´-2´ branch • (3) Cut made at 3´splice site, (3) intron released, & right exon joined to left exon joined -branch site marks 3´ splice site, and is located 18-40 nt upstream of 3´ splice site upstream Lewin Genes VII 2000 Oxford University Press 71 SPLICING SITES SPLICING • yeast branch site consensus: UACUAAC • Consensus branch site not well conserved in higher Consensus eukaryotes: but contains invariant “A” eukaryotes: • Relaxed constraints in higher eukaryotes ---> cryptic Relaxed branch sites used when w.t. branch site deleted branch • Branch site targets the nearest 3´ splice site for joining Branch with the 5´ splice site with 72 TRANSESTERIFICATION TRANSESTERIFICATIO...
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This note was uploaded on 03/26/2014 for the course MBB 321 taught by Professor Davidson during the Spring '11 term at Simon Fraser.

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