Regulon

Regulon is a concept in molecular genetics describing a collection of genes or operons that are regulated by a common regulatory protein or RNA molecule, enabling their coordinated expression under specific conditions. Regulons may include genes scattered across the genome, all governed by the same regulator, rather than a single transcript unit with a shared promoter.

Regulation is typically transcriptional: a regulator binds to DNA regulatory sites near promoters, acting as an activator or repressor. Global regulators can control many operons and pathways, enabling broad responses to environmental signals. In bacteria, examples include the PhoB regulon activated during phosphate limitation; the CRP regulon, controlled by the cyclic AMP receptor protein; the Fur regulon involved in iron homeostasis; and the LexA SOS regulon governing the DNA-damage response.

In eukaryotes, regulon-like concepts describe networks where a transcription factor or chromatin-related regulator coordinates expression of multiple genes, often across different promoters and regulatory contexts. The regulon concept remains useful for organizing a gene set by shared regulation, even as regulatory architectures in higher organisms involve additional layers such as chromatin state and noncoding RNAs.

Regulon boundaries are mapped by genome-scale approaches, including RNA sequencing to profile co-regulated genes and chromatin immunoprecipitation sequencing (ChIP-seq) to identify regulator-binding sites. Comparative genomics and computational network inference help predict regulons, which are then validated by mutant or regulator-overexpression experiments.

Regulons are important for understanding cellular responses, metabolic regulation, and adaptation. They have practical implications in antibiotic development, metabolic engineering, and systems biology, where coordinated control of multiple genes supports robust performance or reveals regulatory weaknesses.