Promoter-proximal elements are necessary for efficient transcription

Point mutations in the promoter and promoter-proximal elements hinder transcription of the β-globin gene. Point mutations throughout the promoter region were analyzed for their effects on transcription rates. The height of each line represents the transcription level relative to a wild-type promoter or promoter-proximal element (1.0). Only the base substitutions that lie within the three elements shown change the level of transcription. Positions with black dots were not tested.

[Data from T. Maniatis, S. Goodbourn, and J. A. Fischer, “Regulation of Inducible and Tissue-Specific Gene Expression,” Science 236, 1987, 1237]