# Regulon

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"Modulon" redirects here. For the spasmolytic, see [Modulon (drug)](/source/Modulon_(drug)). For the birth control pill, see [Ethinylestradiol/desogestrel](/source/Ethinylestradiol/desogestrel).

In [molecular genetics](/source/Molecular_genetics), a **regulon** is a group of [genes](/source/Gene) that are [regulated](/source/Gene_regulation) as a unit, generally controlled by the same [regulatory gene](/source/Regulatory_gene) that [expresses](/source/Gene_expression) a [protein](/source/Protein) acting as a [repressor](/source/Repressor) or [activator](/source/Activator_(genetics)). This terminology is generally, although not exclusively, used in reference to [prokaryotes](/source/Prokaryote), whose [genomes](/source/Genome) are often organized into [operons](/source/Operon); the genes contained within a regulon are usually organized into more than one operon at disparate locations on the [chromosome](/source/Chromosome).[1] Applied to [eukaryotes](/source/Eukaryote), the term refers to any group of non-contiguous genes controlled by the same regulatory gene.[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.[1]

## Examples

Commonly studied regulons in bacteria are those involved in response to stress such as [heat shock](/source/Heat_shock). The heat shock response in *[E. coli](/source/E._coli)* is regulated by the [sigma factor](/source/Sigma_factor) σ32 ([RpoH](/source/RpoH)), whose regulon has been characterized as containing at least 89 [open reading frames](/source/Open_reading_frame).[3]

Regulons involving [virulence factors](/source/Virulence_factor) in [pathogenic](/source/Pathogen) bacteria are of particular research interest; an often-studied example is the [phosphate regulon](/source/Phosphate_regulon) in *[E. coli](/source/E._coli)*, which couples phosphate [homeostasis](/source/Homeostasis) to pathogenicity through a [two-component system](/source/Two-component_system).[4] Regulons can sometimes be [pathogenicity islands](/source/Pathogenicity_island).[5]

The [Ada regulon](/source/Ada_regulon) in *[E. coli](/source/E._coli)* is a well-characterized example of a group of genes involved in the [adaptive response](/source/Adaptive_response) form of [DNA repair](/source/DNA_repair).[6]

[Quorum sensing](/source/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.[1]

## Evolution

Changes in the regulation of [gene networks](/source/Gene_network) are a common mechanism for prokaryotic [evolution](/source/Evolution). An example of the effects of different regulatory environments for [homologous](/source/Homology_(biology)) proteins is the [DNA-binding protein](/source/DNA-binding_protein) [OmpR](/source/OmpR), which is involved in response to [osmotic](/source/Osmotic) stress in *[E. coli](/source/E._coli)* but is involved in response to [acidic](/source/Acid) environments in the close relative [*Salmonella* Typhimurium](/source/Salmonella_Typhimurium).[8]

## References

1. Lengeler, Joseph W. & Postma, P.W. (1999). "Global Regulatory Networks and Signal Transduction Pathways". *Biology of the prokaryotes*. Lengeler, Joseph W.; Drews, Gerhart; Schlegel, Hans G. (eds.). Stuttgart: Thieme. pp. 498–9. ISBN 978-1-4443-1330-7.

1. Nonaka, G; Blankschien, M; Herman, C; Gross, CA; Rhodius, VA (1 July 2006). "Regulon and promoter analysis of the E. coli heat-shock factor, sigma32, reveals a multifaceted cellular response to heat stress.". *Genes & Development*. **20** (13): 1776–89. [doi:10.1101/gad.1428206](https://doi.org/10.1101/gad.1428206). [PMC 1522074](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1522074). [PMID 16818608](https://pubmed.ncbi.nlm.nih.gov/16818608)

1. Lamarche, MG; Wanner, BL; Crépin, S; Harel, J (May 2008). "The phosphate regulon and bacterial virulence: a regulatory network connecting phosphate homeostasis and pathogenesis.". *FEMS Microbiology Reviews*. **32** (3): 461–73. [doi:10.1111/j.1574-6976.2008.00101.x](https://doi.org/10.1111/j.1574-6976.2008.00101.x). [PMID 18248418](https://pubmed.ncbi.nlm.nih.gov/18248418)

1. Hacker, J; Blum-Oehler, G; Mühldorfer, I; Tschäpe, H (March 1997). "Pathogenicity islands of virulent bacteria: structure, function and impact on microbial evolution.". *Molecular Microbiology*. **23** (6): 1089–97. [doi:10.1046/j.1365-2958.1997.3101672.x](https://doi.org/10.1046/j.1365-2958.1997.3101672.x). [PMID 9106201](https://pubmed.ncbi.nlm.nih.gov/9106201)

1. Landini, P & Volkert, MR (December 2000). "Regulatory responses of the adaptive response to alkylation damage: a simple regulon with complex regulatory features.". *Journal of Bacteriology*. **182** (23): 6543–9. [doi:10.1128/jb.182.23.6543-6549.2000](https://doi.org/10.1128/jb.182.23.6543-6549.2000). [PMC 111391](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC111391). [PMID 11073893](https://pubmed.ncbi.nlm.nih.gov/11073893)

1. Michael Hecker & Stefan Müllner (18 July 2003). [*Proteomics of Microorganisms: Fundamental Aspects and Application*](https://books.google.com/books?id=bclwDYPbJj8C&pg=PA66). Springer Science & Business Media. p. 66. ISBN 978-3-540-00546-9.

1. Quinn, HJ; Cameron, AD; Dorman, CJ (March 2014). "Bacterial regulon evolution: distinct responses and roles for the identical OmpR proteins of Salmonella Typhimurium and Escherichia coli in the acid stress response.". *PLOS Genetics*. **10** (3). [doi:10.1371/journal.pgen.1004215](https://doi.org/10.1371/journal.pgen.1004215). [PMC 3945435](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3945435). [PMID 24603618](https://pubmed.ncbi.nlm.nih.gov/24603618)

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Adapted from the Wikipedia article [Regulon](https://en.wikipedia.org/wiki/Regulon) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Regulon?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.