The accessibility of the promoter regions of prokaryotic DNA is (in many cases) regulated by the interaction of proteins with the sequences termed as

In the operon system, the promoter is generally situated beside the operator genes. In the prokaryotes, the working of promoter region (binding of RNA polymerase) is coordinated by the operator genes, e.g. if operator genes are occupied by the repressor proteins then RNA polymerase does not bind to the promoter gene and there is no transcription.