Lecture 13 - RNA processing

Question 1

What is the process of RNA processing?

Answer 1

Transcription
Capping
Cleavage/polyadenylation
Splicing
Mature messenger RNA is created

Question 2

What is capping?

Answer 2

GTP is added at 5’-5’ by phosphates
There is methylation of the first two nucleotides at 2’

Question 3

What is cleavage/polyadenylation?

Answer 3

Cutting the pre-RNA molecule and adding a poly-A tail to stabilise it

Question 4

What is the process of cleavage/polyadenylation?

Answer 4

1. Cleavage and polyadenylation specificity factor (CPSF) binds to AAUAAA
2. Cleavage stimulatory factor binds to G/U.
3. Cleavage stimulatory factor recruits cleaving factors and poly-A polymerase
4. Cleavage occurs
5. Addition of PolyA occurs

Question 5

What are the signals needed for cleavage/polyadenylation to occur?

Answer 5

AAUAAA
G/U or a U rich region

Question 6

What is pre-mRNA splicing?

Answer 6

It generates multiple transcript isoforms from a single gene

Question 7

How is it defined where splicing will occur?

Answer 7

There are specific sequences within the RNA
- 5’ splice site
- 3’ splice site
- branch point region within the intron

Question 8

What is the basic mechanism of pre-mRNA splicing?

Answer 8

• 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

Question 9

What is the process of the spliceosome assembly pathway?

Answer 9

1. Splicing is catalysed by snRNPs and protein splicing factors
2. U1 binds to the branch donor site
3. U2 recognises it and binds at the branch point
4. U4 U5 U6 are recruited and join, this displaces U1
5. U2 U5 U6 rearrange and form the active site

Question 10

What is alternative splicing?

Answer 10

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

Question 11

What are snRNPs?

Answer 11

Small nuclear ribonucleoprotein particles
The ones involves in splicing are U1 U2 U4 U5 U6