Final answer:
Activator proteins bind to enhancer sequences to upregulate transcription of genes with promoters that weakly bind to RNA polymerase, aided by various transcription factors that interact with promoter-proximal elements.
Step-by-step explanation:
Activator proteins bind to enhancer sequences to upregulate transcription of genes which have weakly binding promoters. These activator proteins enhance the interaction between RNA polymerase and a particular promoter, allowing for efficient transcription initiation even when promoters do not strongly attract RNA polymerase on their own. This regulation can involve multiple transcription factors, including those that bind to promoter-proximal elements like the TATA box or the GC and CAAT boxes. These specific transcription factors can bind to various regions upstream of the gene, including enhancer regions, and through the bending of DNA, they facilitate the formation of the transcription initiation complex. This interaction is essential for the transcription of certain genes, especially in eukaryotic organisms, which require this positive regulatory mechanism to synthesize the necessary proteins for the cell.