Regulon

In molecular genetics, a regulon is a group of genes that are regulated as a unit, generally controlled by the same regulatory gene that expresses a protein acting as a repressor or activator. This terminology is generally, although not exclusively, used in reference to prokaryotes, whose genomes are often organized into operons; the genes contained within a regulon are usually organized into more than one operon at disparate locations on the chromosome. ^[1] Applied to eukaryotes, 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. 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.^[3]

Regulons involving virulence factors in pathogenic bacteria are of particular research interest; a often-studied example is the phosphate regulon in E. coli, which couples phosphate homeostasis to pathogenicity through a two-component system.^[4] Regulons can sometimes be pathogenicity islands.^[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.^[1]

Evolution

Changes in the regulation of gene networks are a common mechanism for prokaryotic evolution. An example of the effects of different regulatory environments for homologous proteins is the DNA-binding protein OmpR, which is involved in response to acidic environments in E. coli but is involved in osmotic stress in the close relative Salmonella Typhimurium.^[8]

References

1. Schlegel, edited by Joseph W. Lengeler, Gerhart Drews, Hans G. (1999). "Global Regulatory Networks and Signal Transduction Pathways". Biology of the prokaryotes. Stuttgart: Thieme. pp. 498–9. ISBN 9781444313307.
2. Regulon at the US National Library of Medicine Medical Subject Headings (MeSH)
3. 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. PMID 16818608.
4. 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. PMID 18248418.
5. 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. PMID 9106201.
6. 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. PMID 11073893.
7. Michael Hecker; Stefan Müllner (18 July 2003). Proteomics of Microorganisms: Fundamental Aspects and Application. Springer Science & Business Media. p. 66. ISBN 978-3-540-00546-9.
8. 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): e1004215. PMID 24603618.