Final answer:
TFIIB can bind immediately after TFIID binds the DNA, playing a key role in forming the pre-initiation complex necessary for RNA polymerase II to initiate transcription in eukaryotic cells.
Step-by-step explanation:
In the initiation phase of eukaryotic transcription, the assembly of the pre-initiation complex is a highly orchestrated process that involves several transcription factors. Following the initial binding of the TFIID (Transcription Factor II D) complex to the DNA promoter region, TFIIB (Transcription Factor II B) plays a crucial role in stabilizing this interaction and facilitating the subsequent steps in complex formation.
TFIIB is the factor that promptly binds to the DNA after TFIID, reinforcing the association between TFIID and the DNA. This stabilization is essential for the recruitment of additional transcription factors and the assembly of a functional pre-initiation complex. TFIIB also acts as a bridge between TFIID and RNA polymerase II, promoting the assembly of the core transcription machinery.
As the pre-initiation complex forms, other transcription factors, including TFIIE, TFIIF, and TFIIH, are sequentially recruited. TFIIE and TFIIF contribute to stabilizing the interactions within the complex, while TFIIH plays a critical role in unwinding the DNA and phosphorylating the C-terminal domain of RNA polymerase II. This series of events prepares the transcription initiation complex for the arrival of RNA polymerase II.
The recruitment of RNA polymerase II marks the completion of the pre-initiation complex. With the collaborative efforts of these basal transcription factors, RNA polymerase II is positioned for transcription initiation. The enzymatic activity of RNA polymerase II, combined with the structural modifications induced by the basal transcription factors, facilitates the local unwinding of the DNA helix and the initiation of RNA synthesis, marking the commencement of transcription. In summary, the stepwise assembly of the pre-initiation complex, initiated by the binding of TFIID and stabilized by TFIIB, is a crucial prerequisite for the initiation of eukaryotic transcription.