Final answer:
The first step in the formation of the preinitiation complex in eukaryotic transcription is the binding of the TATA-binding protein to the TATA box, along with TFIID. This step initiates the assembly of the initiation complex which is essential for recruiting RNA polymerase II for the onset of transcription.
Step-by-step explanation:
The very first step in the formation of the preinitiation complex in eukaryotic transcription is the binding of the TATA-binding protein (TBP) to the TATA box within the promoter region, along with transcription initiation factor IID, or TFIID. This event marks the beginning of the assembly of the necessary proteins that make up the initiation complex.
It is this complex that will recruit RNA polymerase II to the promoter, allowing transcription to begin. Enhancers and transcription factors play significant roles in this process as well, though they are not the primary factors in the initial step of forming the preinitiation complex.
Basal transcription factors are crucial in the formation of the preinitiation complex. This complex, which includes various proteins and RNA polymerase II, is necessary for the initiation of transcription in eukaryotes. The complex of transcription factors and RNA polymerase bound to a promoter is the definition of an initiation complex.
Additionally, the separation of DNA strands requires the unwinding of the double helix, creating a region known as the transcription bubble, a step that comes after the formation of the preinitiation complex.