Polymerase and Signals
Country: United States
Date: January 2005
What controls the RNA to be there to do it's magic?
what would you guess is the controller that guides these
actions....something has to regulate the regulator?
The enzyme, RNA polymerase, synthesizes mRNA using one of the DNA strands
as a template. In bacteria, whether or not a gene can be transcribed into
mRNA is controlled by repressor proteins that sit on the operator region of
the gene. The operator region is where RNA polymerase initiates
transcription of the gene into mRNA. When the repressor protein is attached
to the operator region, it blocks the RNA polymerase molecule from binding
to the operator and no mRNA can be synthesized. The repressor protein can
be knocked off the operator by the presence or absence of certain other
molecules in the cell. For example, when the sugar lactose is present in E.
coli, the repressor protein for the lactose operon, is inactivated and
detaches from the operator gene at which point RNA polymerase can begin
making the mRNA that codes for the synthesis of the enzyme lactase which
catalyzes the digestion or splitting of lactose into glucose and galactose.
This is a negative control mechanism which helps the cell conserve energy.
When there is no lactose around, the cell is not bothering to make lactase.
It is called a negative control mechanism because when the control
mechanism is functioning it shuts down the system, like the high
temperature setting on a thermostat.
Ron Baker, Ph.D.
Click here to return to the Molecular Biology Archives
Update: June 2012