Regulons

A regulon is a collection of genes or operons in a genome that are regulated by a single regulatory protein, RNA molecule, or regulatory signal, allowing coordinated expression in response to environmental or cellular conditions. Unlike an operon, which is a cluster of genes transcribed together, a regulon may comprise genes dispersed throughout the genome and linked by shared regulatory control rather than a single transcript.

Regulation is typically mediated by transcription factors or sigma factors that bind to specific DNA sequences near target promoters, or by regulatory RNAs that affect transcript stability or translation. Regulators can effect positive or negative control and can operate under global or condition-specific programs. The result is a coordinated response that can activate or repress a broad set of genes involved in metabolism, stress response, virulence, or other cellular processes.

Well-known examples include the lac regulon of Escherichia coli, which governs lactose utilization and is controlled by the LacI repressor; the Pho regulon, which governs phosphate acquisition; and the SOS regulon, consisting of DNA repair and damage response genes controlled by LexA/RecA. Global regulons often rely on master regulators that integrate multiple signals (for example, carbon source availability, stress, or nutrient limitation) to reprogram gene expression.

Methods such as transcriptomics, chromatin immunoprecipitation followed by sequencing (ChIP-seq), and motif discovery are used to identify regulons and their target genes, while computational network models help in understanding regulatory architecture and dynamics.