The main difference in transcription initiation between Genes 1, 2, and 3 is the presence of a TATA box in Genes 2 and 3.
The TATA box is a specific DNA sequence that is located near the promoter region of many genes and serves as a binding site for a transcription factor called TFIID, which is essential for transcription initiation.
Gene 1 does not have a TATA box, so it uses a different mechanism to initiate transcription. This mechanism involves a group of transcription factors called initiator proteins. Initiator proteins bind to a specific DNA sequence in the promoter region of Gene 1 and recruit RNA polymerase to the site of transcription initiation.
Another potential difference is the presence of enhancers near Genes 2 and 3. Enhancers are DNA sequences that can increase the level of transcription of a gene. They are often located far away from the promoter region of the gene they regulate. If there are enhancers near Genes 2 and 3, they could contribute to the higher levels of transcription initiation observed for these genes.