[2] A modulon is a set of regulons or operons that are collectively regulated in response to changes in overall conditions or stresses, but may be under the control of different or overlapping regulatory molecules.
The term stimulon is sometimes used to refer to the set of genes whose expression responds to specific environmental stimuli.
The heat shock response in E. coli is regulated by the sigma factor σ32 (RpoH), whose regulon has been characterized as containing at least 89 open reading frames.
[5] The Ada regulon in E. coli is a well-characterized example of a group of genes involved in the adaptive response form of DNA repair.
[6] Quorum sensing behavior in bacteria is a commonly cited example of a modulon or stimulon,[7] though some sources describe this type of intercellular auto-induction as a separate form of regulation.