Question

CTD of RNA pol II: The CDT undergoes a cycle of phosphorylation and dephosphorylation during the course of transcription. Which amino acid is phosphorylated by Cdk7 of TFIIH?

A) Pro5.
B) Tyr2.
C) Ser5.
D) Ser2.

Answer 1

Cdk7 of TFIIH phosphorylates Ser5 on the C-terminal domain (CTD) of RNA polymerase II during the transcription process, making option C) Ser5 the correct answer.

Step-by-step explanation:

The CTD of RNA polymerase II undergoes a cycle of phosphorylation and dephosphorylation during the transcription process. Cdk7 of TFIIH is known to add phosphate groups to specific amino acid residues on the C-terminal domain (CTD) of RNA pol II, which is crucial for the initiation and elongation phases of transcription.

Phosphorylation of the CTD serves to regulate the transcriptional activity of RNA polymerase II and promote the transition from the initiation phase to the elongation phase of transcription.

During the initiation phase, Cdk7 specifically phosphorylates the serine at position 5 (Ser5) of the heptapeptide repeat (Y1S2P3T4S5P6S7) within the CTD of RNA pol II. As such, the correct answer to which amino acid is phosphorylated by Cdk7 of TFIIH is Ser5, making option C) Ser5 the answer to the question posed by the student.