Final answer:
Transcription initiation by RNA polymerase II begins with TFIID binding to the TATA box in the promoter region, followed by recruitment of other transcription factors and RNAP II. RNAP II is then phosphorylated, leading to the activation of the transcription initiation complex and the commencement of transcription. Enhancer regions interact with the complex to augment transcription.
Step-by-step explanation:
The process of transcription initiation by RNA polymerase II (RNAP II) involves multiple steps and components working in concert. Initially, within the promoter region, several bases upstream of the transcriptional start site, we can find the TATA box, which is a DNA sequence containing a series of TATA repeats (consensus sequence 5'-TATAAA-3'). This TATA box serves as the binding site for the transcription factor TFIID, which includes the TATA-binding protein (TBP). Once TFIID binds to the TATA box, it initiates the assembly of a complex of additional transcription factors: TFIIB, TFIIE, TFIIF, and TFIIH.
The complete set of transcription factors forms the preinitiation complex, which subsequently recruits RNAP II to the promoter. When RNAP II binds, it is phosphorylated, which leads to a change in its conformation and initiates the transcription process by separating the RNA polymerase from part of the DNA. This structural change places RNA polymerase in the correct orientation to commence transcription. Furthermore, DNA-bending proteins facilitate the interactions between transcription factors and distant enhancer regions. Enhancers can augment transcription by looping back to the promoter and influencing the assembly of the transcription machinery.