Unusual location and function of the operator in the Escherichia coli galactose operon.

The operator of the gal operon is located about 60 base pairs preceding the startpoints of the transcription of the two gal promoters. This location contrasts with the location of the operator in other phage or bacterial operons where the repressor binds more closely to the respective transcription initiation sites. Models explaining how the repressor-operator interactions may control the two gal promoters are presented.