Repressors and Activators Before discussing our examples of transcriptional regulation in bacteria, we give a brief overview of the types of regulation known to occur and define some of the terms that describe the factors involved. The transcription of bacterial operons is regulated by the products of regulatory genes, which are often proteins called repressors or activators. These regulatory proteins bind close to the operon,s promoter and regulate transcription from the promoter. Sometimes, a regulatory protein can play dual roles and can also perform an enzymatic reaction in the pathway encoded by the operon Because they bind to DNA. repressors and activators often have the helix-turn-helix motif shared by many dna binding proteins Repressors bind to sites called operators and turn off the promoter, thereby preventing transcription of the genes of the operon. Activators, in contrast, bind to activator sites and turn on the promoter, thereby facilitating transcription of the operon genes• Repressors and Activators • Before discussing our examples of transcriptional regulation in bacteria, we give a brief overview of the types of regulation known to occur and define some of the terms that describe the factors involved. The transcription of bacterial operons is regulated by the products of regulatory genes, which are often proteins called repressors or activators. These regulatory proteins bind close to the operon's promoter and regulate transcription from the promoter. Sometimes, a regulatory protein can play dual roles and can also perform an enzymatic reaction in the pathway encoded by the operon. Because they bind to DNA, repressors and activators often have the helix-turn-helix motif shared by many DNA binding proteins . • Repressors bind to sites called operators and turn off the promoter, thereby preventing transcription of the genes of the operon. Activators, in contrast, bind to activator sites and turn on the promoter, thereby facilitating transcription of the operon genes