Question

In what sequence are the serine residues in RNA pol II phosphorylated?

(a) 5->2->7

(b) 2->5->7

(c) 2->7->5

(d) 7->2->5

I have been asked this question in semester exam.

My query is from Transcription in Eukaryotes : RNA Polymerases topic in section Gene Expression : Transcription Prokaryotes of Cytogenetics

Answer 1

Correct option is (c) 2->7->5

The explanation is: The phosphorylation is at the 2^nd serine residue with the help of the TFIIH, and then during elongation the phosphorylation is at the 5^th serine residue. Between these two there is a short phase of phosphorylation at the 7^th serine.