Negative and Positive regulation Another important concept is the distinction between negative and positive regulation by regulatory proteins. If a regulatory protein in its active state turns off the expression of the operon, the operon is said to be negatively regulated by the regulatory protein. If the regulatory protein in its active state turns on the operon, the operon is positively regulated by the regulatory protein. An operon regulated by a repressor is therefore negatively regulated, because the presence of the active repressor prevents transcription of that operon. In contrast an operon regulated by an activator is positively regulated because in its active state the activator protein turns on transcription of the operon under its control Activator and repressor proteins usually bind to different regions of the dna• Negative and Positive Regulation • Another important concept is the distinction between negative and positive regulation by regulatory proteins. If a regulatory protein in its active state turns off the expression of the operon, the operon is said to be negatively regulated by the regulatory protein. If the regulatory protein in its active state turns on the operon, the operon is positively regulated by the regulatory protein. An operon regulated by a repressor is therefore negatively regulated, because the presence of the active repressor prevents transcription of that operon. In contrast, an operon regulated by an activator is positively regulated, because in its active state the activator protein turns on transcription of the operon under its control. • Activator and repressor proteins usually bind to different regions of the DNA