Final answer:
In eukaryotes, repressor proteins bind to operators to block gene expression.
Step-by-step explanation:
In eukaryotes, the ability to switch gene expression on or off is achieved through the binding of a repressor protein to a DNA sequence called an operator. The repressor protein blocks gene expression by physically preventing the transcription process. This is in contrast to prokaryotes, where repressors bind to operator regions near the genes they control.