Bacterial multidrug resistance (MDR) is a serious and pressing threat to public health. The emrRAB operon encodes a pump that can extrude, using proton motive force, several structurally unrelated drugs from Escherichia coli, e. g., protonophores and the antibiotics thiolactomycin and nalidixic acid (NA). The EmrB protein pumps the drugs across the cytoplasmic membrane; EmrA probably facilitates passage through the periplasm; and a third, as yet unidentified protein transports it through the outer membrane. The emrRAB operon, which has a signma70 type promoter, is negatively regulated by the product of one of its own genes, namely, emrR. The pump is induced by a variety of structurally unrelated drugs, many of which are also the substrates it transports. Based on the information above answer the following questions. Fill in the blanks in the DNA with the letter codes that represent the following sequence elements. a. Promoter b. emrR binding site c. Shine-Dalgarno site d. Transcription terminator