Strong promoters usually require
Strong promoters possess near-perfect -35 TTGACA and -10 TATAAT hexamers separated by optimal 17 base pair spacer including AT-rich UP element interacting with alpha C-terminal domain, producing exceptionally high intrinsic affinity for sigma70 holoenzyme and spontaneous open complex formation. Uncontrolled activity would wastefully consume nucleotides, ribosomes, and energy producing unnecessary transcripts. Evolution pairs potent cores with repressor proteins whose operators overlap start site, creating steric block until specific signal inactivates repressor. Net effect is high regulatory r
Ref: Alberts Molecular Biology of the Cell – strong promoters require repressors to prevent wasteful constitutive transcription.
