Splicing Flashcards
What causes recognition of the intron
U1 SNRNP recognizes sequence at 5’ end of intron. BBP and U2AF bind to the A branch point site.
What is the second step?
U2 snRNP then replaces BBP and U2AF at branch point A.
What now enters the reaction?
U4/U6/U5 triple snRNP binds causing the creation of the active site of the spliceosome.
- also positions appropriate portions of pre-mRNA substrate for the first phosphoryl-transferase reaction.
How is the lariat formed?
U1 and U4 leave, lariat forms along with 5’ splice site sequence. U6 and U2 still present with U5.
How is the lariat released?
3’ splice site cleavage, lariat is released, exon 1 connected to exon 2.
Active site for second phosphoryl-transferase reaction is formed, completing the splice.
What does binding my u1 snrnp and u6 snrnp do?
Ensures proper splice site selection.
what does binding by bbp and u2 snrnp do?
ensures splicing accuracy
What do the two phosphoryl transfer reactions do?
Lariat Formation • Joining of exons
What causes RNA processing?
-Dephosphorylation at Ser5 recruits 3’ end processing proteins,
What occurs in RNA processing?
- Cleavage Stimulating Factor (CstF) and Cleavage and Polyadenylation Specificity Factor (CPSF) are bound to the RNA polymerase tail.
CstF and CPSF recognize and bind a specific 3’ processing sequence
What are the steps of cleavage and polyadenylation?
CstF and CPSF assemble additional factors required for cleavage.
• RNA is cleaved.
Poly-A binding proteins bind the poly-A
tail.
What do poly-a binding proteins do?
Poly-A binding proteins determine the length of the tail and direct protein synthesis.
What has mature mRNA done?
It has undergone capping, splicing, and polyadenylation.
How is mrna exported out of nucleus?
Small molecules move through pore freely. Larger molecules need to bind a nuclear transport receptor to help it move in/out (including mRNAs)
How is rrna transcribed?
-Transcribed by RNA polymerase 1. RNAP 1 doesn’t have a C-terminal tail, and therefore rRNAs aren’t capped or polyadenylated.
-Assembled into ribosomes in
nucleolus.
