MBB 222 Lecture Notes - Lecture 30: Phosphodiester Bond, Spliceosome, Transesterification
20 Dec 2018
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Document Summary
Splice sites in spliceosome-mediated introns are conserved in eukaryotes. Ag/gu and ag/g sequences mark where splicing will occur (at the down arrows). E1 is exon 1, aka the 5" exon; e2 is exon 2, aka the 3" exon. The central branch-site adenosine is located toward the 3" end of the intron. Spliceosome-mediated splicing reaction: the 2-oh of branch site a nucleophilically attacks the 5" phosphate of the 1st nucleotide of the intron. This cleaves the phosphodiester bond between the intron and the upstream exon and forms a new 2"-5" phosphodiester bond between a and the intron. The spliceosome is a highly conserved structure made up of the mrna to be spliced plus >200 proteins and 5 small nuclear rnas (snrnas are each 100-200 nucleotides long, made by rna polymerase ii). The snrnas associate with spliceosome proteins to form specialized rna- protein complexes, small nuclear ribonucleoproteins (snrnps or snurps ). U2, u4, u5 and u6) are involved in splicing reactions.
