Proteins

The correct answer is option (E): Promoter, operator, and structural genes
"Operons are made up of several genes arranged in a group with a promoter and an operator. Prokaryotes have optorons, but eukaryotes do not. When more than one operon is regulated by the same regulatory protein, the operons collectively make up a regulon. An operon has three fundamental parts.
1. Promoter: The region upstream of where RNA polymerase attaches.
2. Operator: A DNA segment to which a repressor protein attaches and prevents RNA polymerase from working to promote transcription.
3. Genes that are collectively controlled by an operon are known as structural genes."