The right answer is the promoter.
• The promoter is a nucleotide sequence that allows the transcription of the gene into mRNA. It is recognized by the RNA polymerase that initiates transcription. During the synthesis of the RNA, the promoter indicates which gene must be expressed and therefore which proteins the cell must produce. In an operon it is common to all genes.
• The operator is a segment of DNA and / or messenger RNA to which a chemical signal (a regulatory molecule) binds. It can be either a repressor signal or a transcription activating signal (DNA operator) or translation (RNA operator) of the genes of the operon. The RNA polymerase does not recognize this structure.
