Lecture 13 - RNA processing Flashcards
What is the process of RNA processing?
Transcription
Capping
Cleavage/polyadenylation
Splicing
Mature messenger RNA is created
What is capping?
GTP is added at 5’-5’ by phosphates
There is methylation of the first two nucleotides at 2’
What is cleavage/polyadenylation?
Cutting the pre-RNA molecule and adding a poly-A tail to stabilise it
What is the process of cleavage/polyadenylation?
- Cleavage and polyadenylation specificity factor (CPSF) binds to AAUAAA
- Cleavage stimulatory factor binds to G/U.
- Cleavage stimulatory factor recruits cleaving factors and poly-A polymerase
- Cleavage occurs
- Addition of PolyA occurs
What are the signals needed for cleavage/polyadenylation to occur?
AAUAAA
G/U or a U rich region
What is pre-mRNA splicing?
It generates multiple transcript isoforms from a single gene
How is it defined where splicing will occur?
There are specific sequences within the RNA
- 5’ splice site
- 3’ splice site
- branch point region within the intron
What is the basic mechanism of pre-mRNA splicing?
- There is cleavage at the 5’ splice site
- Lariat formation at the branch point sequence
- Cleavage at the 3’ splice site
- The intron region is removed
- Exons are ligated
What is the process of the spliceosome assembly pathway?
- Splicing is catalysed by snRNPs and protein splicing factors
- U1 binds to the branch donor site
- U2 recognises it and binds at the branch point
- U4 U5 U6 are recruited and join, this displaces U1
- U2 U5 U6 rearrange and form the active site
What is alternative splicing?
Exons are joined in different combinations
There is inclusion or exclusion of exons
Different proteins can be made from a single gene and may have different functions
What are snRNPs?
Small nuclear ribonucleoprotein particles
The ones involves in splicing are U1 U2 U4 U5 U6
