Much of the research in gene regulation has been accomplished with prokaryotes, and especially with the common bacterium, Escherichia coli. So it is useful to look at some of the prokaryotic gene regulatory controls before trying to see how genes can be regulated in the cells of eukaryotic organisms. A typical gene is reasonably complex. In addition there will be a regulator gene. These are collectively known as the operon .
Activators bind to DNA making it easier for RNA polymerase to attach to the promoter.
Promoter Recognized by RNA polymerase as the place to start transcription Operator Controls RNA polymerase's access to the promoter Structural Gene Codes for the needed protein Some operons are always functional in the cell. The Lactose Operon Example of Prokaryotic Gene Regulation Negative Control using a repressor. Operons were first shown with E. coli , and the gene which codes for the enzyme, lactase. Once the promoter is available, the genes which code for the enzymes to digest lactose are transcribed. When the enzyme, lactase is synthesized, the lactose is degraded.