Which of the following are promoter elements in bacteria?

• A. -40 TTGACA and -15 TATAAT
• B. TATA box and CAAT box
• C. -75 TTGCAA and -20 TATAAT
• D. -60 TTGACA and -20 TATAAT

Answer: (C)

Promoter elements in bacteria are DNA sequences located upstream of the transcription start site that guide RNA polymerase binding through recognition by sigma factors. The classic signals are a -35 region with a TTGACA-like motif and a -10 region with a TATAAT-like motif, spaced so RNA polymerase can properly initiate transcription. Some promoters show variations or additional elements, such as a -75 region that resembles the -35 motif or an extended -10 region that includes a motif near the -10 area, which helps sigma factors bind when the -35 signal isn’t strong.

The best choice reflects this pattern by giving a -75 position with a TTGCAA sequence (similar to the -35 motif) and a -20 position with TATAAT (a close relative of the -10 motif seen in extended -10 promoters). This demonstrates the presence of recognizable bacterial promoter elements, just located at slightly different upstream positions, which is consistent with how promoters can vary among bacteria and among different sigma factors.

The other options either point to promoter features typical of eukaryotes (like a TATA box and CAAT box) or place canonical promoter signals at nonstandard distances that aren’t characteristic of bacterial promoters, so they don’t fit as accurate bacterial promoter elements.