Question

CTD of RNA pol II: Which amino acid is phosphorylated by pTEFb during the elongating phase of transcription? (Note: this is not what TFIIH does.)

A) Ser5.
B) Pro3.
C) Tyr5.
D) Ser2.

Answer 1

The amino acid phosphorylated by pTEFb during the elongation phase of transcription by RNA polymerase II is Ser2, which is essential for transitioning from initiation to elongation and for mRNA synthesis progression.

Step-by-step explanation:

The correct option : d

Which amino acid is phosphorylated by positive Transcription Elongation Factor b (pTEFb) during the elongating phase of transcription by RNA polymerase II is Ser2. The C-terminal domain (CTD) of RNA polymerase II contains a repetitive sequence of tyrosine, serine, proline, threonine, serine, and another serine (YSPTSPS). Phosphorylation is particularly important at serine positions 2 and 5.

TFIIH is known to phosphorylate Ser5 during the initiation phase, whereas during the transition to the elongation phase, pTEFb specifically targets Ser2 for phosphorylation. This phosphorylation event leads to the release of some of the initiating transcription factors and allows RNA polymerase II to proceed with mRNA elongation.During the elongating phase of transcription, pTEFb phosphorylates the serine amino acid at position 2 (Ser2) of RNA polymerase II.