Practice question

Promoter anatomy reveals two conserved hexamers spaced seventeen base pairs apart. Upstream hexamer centered around -35 position consensus sequence TTGACA contacted by sigma70 region 4 helix-turn-helix domain. Downstream Pribnow box at -10 consensus TATAAT recognized by region 2. Spacer length crucial for simultaneous contact of both elements due to helical phasing. TTGACA sequence unambiguously defines -35 element, distinguishing it from -10, UP element recognized by α-CTD, or GC-rich eukaryotic SP1 site GGGCGG. Promoter strength correlates with closeness to TTGACA consensus for -35 interaction optimizing closed complex formation.