Final answer:
Enhancer sequences are regions that can increase the rate of gene transcription and are located variably in relation to the genes they regulate. They can be upstream, downstream, within the gene's coding region, thousands of nucleotides away, or on another chromosome and interact with promoters through a three-dimensional DNA structure.
Step-by-step explanation:
Enhancer sequences are critical elements in the regulation of gene expression in eukaryotic organisms. These enhancer regions are unique because they do not have fixed locations relative to the genes they regulate. Enhancers can function irrespective of their position, whether they are upstream, within the coding region, or downstream of a gene. They can even be located thousands of nucleotides away from the gene or, in some rare cases, on another chromosome entirely. Enhancers contain short DNA sequences known as distal control elements, where activators bind. The bound activators interact with mediator proteins and transcription factors at the promoter region, which facilitates the formation of the preinitiation complex and eventually leads to an increase in transcription of the associated gene.
When transcription factors bind to enhancers, they cause the DNA to bend, allowing distant enhancers to come into physical contact with the promoter regions of their target genes. This three-dimensional configuration is key to enhancer function, enabling enhancers to control gene expression even when they are not close to the promoter on the linear DNA sequence.