The promoter element known as the Pribnow box is located at which position relative to the transcription start site?

• A. -35
• B. -10
• C. +1
• D. +10

Answer: (B)

The Pribnow box is a bacterial promoter element that sits about ten bases upstream of where transcription starts. This position helps RNA polymerase, with its sigma factor, recognize the promoter and unwind the DNA to form the open complex so transcription begins at the first nucleotide. It’s located before the transcription start site, not at it or downstream into the coding region. Another promoter feature lies farther upstream, around thirty-five bases before the start, aiding sigma factor binding. The transcription start site itself is the +1 position where RNA synthesis begins, so it is not the Pribnow box.