18.01.08 Splicing Flashcards Preview

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When and where does splicing occur?

In the nucleus pre-mRNA is processed to form mature RNA following 5' capping, 3' polyadenylation and splicing.


Summarise splicing.

Removal of introns by endonucletolytic cleavage and ligation of exons.


How is splicing mediated?

By the major and minor spliceosomes; complexed of snRNA molecules and >100 proteins.

Major snRNAs: U1 U2 U4 U5 and U6
Minor snRNAs: U11 U12, U4atac, U5 and U6atatc


What is the GT-AG rule

Introns begin with GT (GU) and end with a AG.


What are the sequential steps of pre-mRNA interactions with the snRNA complex?

1. U1 snRNA binds to donor splice site (“GU”) (via it’s complementary sequence: UACUUAC)

2. U2 snRNA binds to branch site (“A” nucleotide), U1 and U2 come together forming a loop in the pre-mRNA

3. U4, U5 & U6 associate with U1-U2 to form the spliceosome; U5 binds both donor & acceptor splice sites

4. Nucleophilic attack of GU (donor) by 2’ hydroxyl group of A of branch point, transesterification #1 (covalent link) forms lariat

5. Cleavage of acceptor (“AG”) transesterification #2 joins exons together

6. Lariat intron & spliceosome unbound