Final answer:
Activators and repressors interact with DNA's major groove through a specific domain to bind to particular DNA sequences and regulate transcription.
Step-by-step explanation:
Activators and repressors often have a domain that interacts with the major groove of the DNA helix, permitting binding to a specific sequence of DNA. These regulatory proteins influence gene expression by either enhancing or repressing the transcription process. Activators are proteins that enhance the interaction between RNA polymerase and a specific promoter, facilitating transcription initiation. On the other hand, repressors bind to non-coding sequences close to or overlapping with the promoter region, thereby impeding the transcription process. Both activators and repressors bind to DNA via specific motifs such as the helix-turn-helix, zinc finger, or leucine zipper. These interactions are essential for the precise regulation of gene expression in response to various internal and external stimuli.