Final answer:
Transcriptional initiation is mediated by the direct interaction between RNA polymerase and the promoter DNA sequence. The two types of transcriptional initiation processes are prokaryotic and eukaryotic, with prokaryotes having a simpler initiation mechanism compared to eukaryotes.
Step-by-step explanation:
The direct interaction that mediates transcriptional initiation is between RNA polymerase and the promoter DNA sequence. RNA polymerase binds to the promoter, which is a specific DNA sequence, to initiate transcription.
There are two types of transcriptional initiation processes:
- Prokaryotic transcriptional initiation: In prokaryotes, initiation is mediated by the binding of RNA polymerase directly to the promoter DNA sequence.
- Eukaryotic transcriptional initiation: In eukaryotes, initiation is more complex and involves the assembly of a large transcription initiation complex. Transcription factors recognize the promoter sequence and recruit RNA polymerase II to form the initiation complex.