Regulation of the operon switches
Operon regulation can be described based on whether the operon is switched on or off under normal conditions:
Inducible operons are normally switched off. The gene is usually not expressed and is only activated (induced) under certain environmental conditions.
Repressible operons are normally switched on. The gene is usually expressed and only inhibited (repressed) under certain environmental conditions.
The gene regulation of operons is described as both positive or negative, and inducible or repressible. Positive and negative refer to the type of regulator, while inducible and repressible refer to the conditions in which the gene is normally expressed.
Operons cannot be both positive and negative, or inducible and repressible.