Final answer:
Enhancers are DNA sequences that bind activators to boost transcription efficiency from a distance, while promoters are DNA sequences located upstream of genes that initiate transcription by binding RNA polymerase and general transcription factors.
Step-by-step explanation:
Enhancers and promoters play critical roles in the regulation of gene expression. While they are both involved in the process of initiating transcription, they have distinct functions and are not interchangeable. Enhancers are DNA sequences that can be located upstream, downstream, or even within the gene they regulate and can be thousands of nucleotides away from the gene. They serve as binding sites for specific transcription factors known as activators. These activators, once bound, can increase the efficiency of transcription by interacting with the transcription initiation complex at the promoter through a DNA-bending mechanism. This allows for long-range regulation of gene expression.
Promoters, on the other hand, are located upstream of the gene and are essential for the initiation of transcription. They directly bind general transcription factors and RNA polymerase to recruit them to the correct site for transcription to begin. Unlike enhancers, promoters are necessary for the transcription machinery to correctly assemble and to start transcribing the gene into RNA. Both enhancers and promoters can also be the target of repressors, which are proteins that can inhibit transcription.
In summary, the main difference is that enhancers boost the rate of transcription from afar by bending the DNA to facilitate interactions, whereas promoters initiate transcription by directly assembling the transcription machinery at the gene's start site. It's also noteworthy that contrary to one of the options, enhancers do not bind RNA polymerase to initiate transcription, and promoters are not proteins, but are specific DNA sequences.