Final answer:
Eukaryotic transcription regulators affect transcription from a distance by DNA looping, which allows enhancers to interact with promoter regions. Activators and repressors bound to these enhancers regulate transcription by enhancing or silencing gene expression, respectively.
Step-by-step explanation:
Most eukaryotic transcription regulators are able to affect transcription even when their binding sites are far from the promoter due to the structure and flexibility of DNA. Transcription factors bind to enhancers, which can be located far from a gene's promoter. The DNA between the enhancer and promoter loops out, allowing these bound factors to interact with the basal transcription machinery at the promoter. This interaction is facilitated by bending and looping of the DNA, which brings these distant regulatory elements into close proximity with the preinitiation complex, including RNA polymerase II and other transcription factors at the promoter.
Enhancers can serve as binding platforms for activator proteins that enhance transcription when they are in proximity to a gene's promoter. Conversely, repressors can bind to these or separate enhancer regions and block transcription. These regulatory mechanisms demonstrate the complexity of eukaryotic transcription control, which involves an interplay between enhancers, silencers, and a wide array of other regulatory elements and proteins.