Post-Transcriptional Processes

Question 1

Purposes of 5’ capping

Answer 1

Splicing of 5’-proximal introns
Export to cytoplasm
Xrn1 degradation prevention
Translation initiation

Question 2

Process of 5’ capping

Answer 2

RTPase removes g-phosphate from 5’-end
RGTase transfers GMP
Methylation by Guanine-N7-RNA-methyltransferase from S-Ado-Met
Bound by CBC in the nucleus

Question 3

Recruitment of 5’ capping enzymes - and supporting proof

Answer 3

S5 phosphorylation of RNA Pol by TFIIH

In vivo -
truncated CTD and mutant CTD have no capping activity
But mutant CTD fused to capping enzymes DOES!

In vitro - WT CTD and mutant CTD have no capping activity, only phosphorylated CTD has.

Question 4

Polyadenylation sequence

Answer 4

AAUAAA-10-30nt - [] - <30nt - GU/U-rich region

Question 5

Polyadenylation process

Answer 5

CPSF binds AAUAAA, CstF binds G/U-rich region