Regulation of gene expression
Gene regulation controls when and how much protein is made.
Cells control which genes are turned on or off through a process called gene regulation—a suite of mechanisms that ramp up or dial down the production of specific RNA or protein molecules. This ability is vital for viruses, bacteria, and complex organisms, because it lets a cell make proteins only when they are needed, boosting the organism’s flexibility and adaptability. In nature, elaborate gene regulation programs guide things like embryonic development, responses to changes in the environment, and the switch to new food sources.
Virtually every step of gene expression can be tweaked, from the initial signal that starts transcription all the way to modifications made to a protein after it’s built. The most common control point is the very beginning of transcription itself. Often, one regulator controls another, forming a cascade known as a gene regulatory network.
The first recognized example of such a system was the *lac* operon, identified in 1961 by François Jacob and Jacques Monod in *E. coli*. In this system, enzymes for digesting lactose are produced only when lactose is present and glucose is absent. (Earlier, in 1951, Barbara McClintock had shown interactions between two genetic loci—Activator and Dissociator—in maize seed color, but the *lac* operon is widely considered the first formal discovery of gene regulation.)
In multicellular organisms, gene regulation drives cellular differentiation and the shaping of the embryo. Different cell types arise from the same genome by expressing different sets of genes. While this doesn’t explain how gene regulation itself originated, evolutionary biologists see it as a key part of how evolution works at the molecular level, and it is central to the field of evolutionary developmental biology (“evo-devo”).
Regulation can occur at many stages: signal transduction, chromatin structure and remodeling, transcription, post-transcriptional modification, RNA transport, translation, and mRNA degradation. In eukaryotes, the accessibility of large DNA regions depends on chromatin structure, which can be altered by histone modifications directed by DNA methylation, non-coding RNA, or DNA-binding proteins. These modifications can turn genes up or down, and some are inheritable, a phenomenon called epigenetic regulation.
The density of DNA packing generally reflects how often a gene is transcribed. Histone proteins,
- field
- Molecular biology, genetics
- known_for
- First discovery of a gene regulation system: the lac operon (1961)
- key_mechanisms
- Transcriptional initiation, RNA processing, post-translational modification, chromatin remodeling, DNA methylation, histone acetylation, microRNA, long non-coding RNA
Lore & Background
The first discovery of a gene regulation system is widely considered to be the identification in 1961 of the lac operon, discovered by François Jacob and Jacques Monod, in which some enzymes involved in lactose metabolism are expressed by E. coli only in the presence of lactose and absence of glucose. As early as 1951, Barbara McClintock showed interaction between two genetic loci, Activator (Ac) and Dissociator (Ds), in the color formation of maize seeds. Regulation of transcription controls when transcription occurs and how much RNA is created, involving specificity factors, repressors, general transcription factors, activators, enhancers, and silencers.
Reader's Guide
Gene regulation is central to the science of evolutionary developmental biology ('evo-devo') and provides a partial explanation of how evolution works at a molecular level. In multicellular organisms, gene regulation drives cellular differentiation and morphogenesis in the embryo, leading to the creation of different cell types that possess different gene expression profiles from the same genome sequence. Epigenetic modifications, such as DNA methylation and histone acetylation, are inheritable and can up or down regulate gene expression. Abnormal methylation patterns are thought to be involved in oncogenesis, and transcriptional silencing by CpG island methylation may be more important than mutation in causing progression to cancer. Long non-coding RNAs are potential biomarkers and may be useful targets for drugs or gene therapy, although no approved drugs target them yet.
Did You Know?
- The first discovery of a gene regulation system is widely considered to be the lac operon, identified in 1961 by François Jacob and Jacques Monod.
- Barbara McClintock showed interaction between two genetic loci, Activator (Ac) and Dissociator (Ds), in maize seed color formation as early as 1951.
- In colorectal cancers, about 600 to 800 genes are transcriptionally silenced by CpG island methylation.
- Long non-coding RNAs (lncRNAs) are potential biomarkers and may be useful targets for drugs or gene therapy, though no approved drugs target them yet.
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