Final answer:
The Lac repressor protein's DNA-binding domain is characterized by the helix-turn-helix motif, which allows for specific DNA interactions to regulate gene expression.
Step-by-step explanation:
The DNA-binding domain of the Lac repressor protein has a characteristic three-dimensional structure known as the helix-turn-helix motif. In the context of gene regulation, particularly the regulation of the lac operon, the Lac repressor protein can bind to operator DNA sequences to prevent transcription. The helix-turn-helix motif of the protein enables it to recognize and bind specific sequences of DNA by fitting into the major groove of the DNA double helix.
Other DNA-binding motifs and domains commonly found in regulatory proteins include the zinc finger domain and the leucine zipper motif, as well as the homeodomain, each with a distinct structure allowing for specific interactions with DNA to regulate gene expression.