The specific sequence of the promoter determines the strength of the promoter (a strong promoter leads to a high rate of transcription initiation).

In addition to sequences that “promote” transcription, a promoter may include additional sequences known as operators that control the strength of the promoter.

Sometimes, we ignore the details of how a promoter works and think of a promoter as a device that converts inputs into outputs. You can do this when designing a multi-component system that includes promoters whose activity must be regulated by other species in the system.