W1 L2 RNA Processing T

Question 1

Transcript Processing

Answer 1

-Primary transcript (heterogeneous nuclear RNA, hnRNA) is coordinately processed in the nucleus
RNApol II recruits of RNA processing enzymes via CTD
Repeats of 7 aa’s in C-terminus of large RNApol II subunit is Phosphorylated by general transcription factors leading to recruitment

Question 2

Tail phosphorylation and stage

Answer 2

no phosphorylation: pre-initiation
phosphorylation at 5th aa: promoter escape, capping
phosphorylation at 2nd and 5th: elongation, splicing
phosphorylation at 2nd: termination, 3’ end modification

Question 3

Formation of the 5’ mRNA cap

Answer 3

3 enzyme recruited by c terminal domain
RNA triphosphatase :Removal of gP from hnRNA
Guanylyltransferase: Condensation of GTP-hnRNA
! Methyltransferase :Methylation of N7

Question 4

Why do we need to modify mRNA

Answer 4

• increase stability,
• 5’ cap useful for circularise, important for translation
  -N7 allow for better recognition of our own RNA vs RNA from other sources

Question 5

Transcription Termination

Answer 5

• At the end of the DNA sequences is a poly A sequence( AAUAAAA)
• CstF and CPSF bind to polyA signal sequences in RNA cleave the RNA, CstF then leave the complex
• the Poly-Apolymerase (PAP) then bind to the 3’ of rna and start adding A, up to 200
  -poly A binding protein attach to the tail causing PAP and CPSF to leave

Question 6

What is the role of 3’ a tail

Answer 6

Stability, lack of A can lead to degradation

Question 7

Aftermatch of termination dealing with runaway transcription

Answer 7

Phosphotate to stop transcription process
The remainder tail is bind by a particular protein which degrade the rna faster than elongation (torpedo)
Or cleavage lead to unstable the sequence (allosteric)

Question 8

What does the splicosome complex consist of

Answer 8

! ~150 proteins
! 5 small nuclear RNAs (U1, U2, U4/U6, U5 snRNAs)
! snRNAs associate with proteins to form snRNPs (small nuclear
ribonucleoproteins, ‘snurps’)

Question 9

Role of snRNPs

Answer 9

-bind in succession to pre-mRNA
! 1. Recognise the 5’splice site and branch site to Determine specificity of splicing
! 2. Bring together the 5’splice site and the branch site
! 3. Catalyse RNA cleavage and joining reactions

Question 10

Splicing process

Answer 10

The branch site A attach to the 5’ end purine forming a lariat
At the purine at the 3’ end is cleaved
The extrinsic are then brought togheter

Question 11

In-depth splicing process

Answer 11

U1 normally bind to the 5’ of the intron, this is then connected to the u6
BBp bind to branch site, then is replaced by U2
U6 and U2 bring the exon together creating lariat (bio chem bs leading to cleavage)
U5 join exon together

Question 12

Splicing error consequences

Answer 12

thalassemia diseases

Question 13

How to ensure correct splicing

Answer 13

! Proteins can interact with introns and exons to help define these and assist in accurate splicing
! This is particularly important for genes with very large introns

Question 14

Three types of RNA splicing

Answer 14

• majority are u2 u6 splicing
  Rare u12 and u11 snRNA which recognize different intron base (1%)

Question 15

Trans-splicing

Answer 15

Joining two gene by splicing 2 gene
Need one 5’ and 3’ with branch on the other gene
Trick the splicesosome to cut and join the two gene together

Question 16

Example of trans splice

Answer 16

! Generally trans-splicing is rare BUT in Trypanosomes all mRNAs are trans-spliced
! Allows a common region to be attached

Question 17

OTrans-splicing in C. elegans

Answer 17

mRNAs are trans-spliced to attach a 5’leader sequence
! polycistronic pre-mRNAs: cleaved, cis-spliced into polycistronic and trans-spliced
The leader cause the final product to be express in different area
Final product are called outron