MBB331_Week11-Fall-2011

Press 6 u2u6 splicing u2u6 u6 and u4 snrnps u6 are

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Unformatted text preview: d) “A” • “B1 complex”: U5 & ”: U4/U6 snRNPs bind U5 binds 5´ exon splice site splice U6 U5 Lewin Genes VII 2000 Oxford University Press 6 “U2/U6 SPLICING”: U2/U6 • U6 and U4 snRNPs U6 are paired before joining spliceosome 26 nucleotides of U6 paired with 2 separate regions of U4 regions • role of U4 is to role sequester U6 until needed needed • U6 later binds U2 and U6 the resulting RNA structure catalyzes splicing splicing Lewin Genes VII 2000 Oxford University Press 7 SPLICEOSOME COMPONENTS SPLICEOSOME COMPONENTS • “B2 complex”: U1 B2 release causing repositioning: U5 at exon ---> intron; U6 binds 5´ splice site; • “C1 complex”: ATP C1 hydrolysis & U4 release triggers U2/U6 catalyzed transesterification making 5´-2´lariat (“A” in branch site attacks 5´splice site, creating lariat and cleaving 5´splice site) site) U6 U5 Lewin Genes VII 2000 Oxford University Press 8 SPLICEOSOME COMPONENTS SPLICEOSOME COMPONENTS • “C2 complex”: ATP C2 hydrolysis again & spliceosome complex moves for exon-exon transesterification, ligating exons and releasing intron releasing U6 U5 Lewin Genes VII 2000 Oxford University Press 9 SUMMARY: snRNAs PAIRING SUMMARY: snRNAs PAIRING WITH pre­mRNA SITES • (1) U1 snRNA hybridizes with (1) the 5´ splice site the • (2) U2 snRNA pairs with the (2) branch site branch • (3) U6 snRNA hybridizes with (3) the 5´splice site the • (4) U5 snRNA brings both (4) exons together by RNA binding binding Lewin Genes VII 2000 Oxford University Press 10 THE SPLICEOSOME CYCLE THE =E 11 Weaver 2002 Molecular Biology Ed. 2 NUCLEAR SPLICING: AN OVERVIEW OVERVIEW Lodish et al. 2000. Molecular Cell Biology 4.0. Ed. W.H. Freeman and Co. Lodish et 12 Other contributors to splicing -we have seen that eukaryotic mRNAs are generally capped and polyadenylated and there is evidence that both these modifications contribute to splicing -in vitro studies indicate that cap may be required for removal of 1st intron, whereas poly(A) tail may be required for removal of last intron -paper published in Genes & Development demonstrates even RNA Pol II can have role in splicing -recall RNAP phospho...
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