Question

Q: Describe how CTD phosphorylation affects transcription?

Answer 1

Ans) 1) Phosphorylation of CTD helps in the transition from initiation to elongation step in Eukaryotes -The last step in the eukaryotic transcription initiation (particularly last step in the assembly of initiation complex) is the phosphorylation of CTD (C-terminal domain) of largest subunit of RNA Polymerase-II. Only when CTD is phosphorylated, the RNA polymerase will leave the pre-initiation complex and to start elongation step.

2) Mediator complex which is bound to CTD regulates TFIIH activity. Mediator complex also help RNA polymerase to interact with DNA bound activator proteins.

3) Phosphorylation of serine-5 at CTD helps in recruitment of capping factors and Serine-2 phosphorylation recruit splicing factors . Thus,the phosphorylation of CTD is also required for the Elongation step of transcription in Eukaryotes.