A regulator gene, regulator, or regulatory gene is a gene

Gene

A gene is a molecular unit of heredity of a living organism. It is a name given to some stretches of DNA and RNA that code for a type of protein or for an RNA chain that has a function in the organism. Living beings depend on genes, as they specify all proteins and functional RNA chains...

 involved in controlling the expression

Gene expression

Gene expression is the process by which information from a gene is used in the synthesis of a functional gene product. These products are often proteins, but in non-protein coding genes such as ribosomal RNA , transfer RNA or small nuclear RNA genes, the product is a functional RNA...

 of one or more other genes. A regulator gene may encode a protein, or it may work at the level of RNA

RNA

Ribonucleic acid , or RNA, is one of the three major macromolecules that are essential for all known forms of life....

, as in the case of genes encoding microRNAs.

In prokaryotes, regulator genes often code for repressor proteins. Repressor proteins bind to operator

Operator (biology)

In genetics, an operator is a segment of DNA to which a transcription factor protein binds. It is classically defined in the lac operon as a segment between the promoter and the genes of the operon. In the case of a repressor, the repressor protein physically obstructs the RNA polymerase from...

s or promoters, preventing RNA polymerase

RNA polymerase

RNA polymerase is an enzyme that produces RNA. In cells, RNAP is needed for constructing RNA chains from DNA genes as templates, a process called transcription. RNA polymerase enzymes are essential to life and are found in all organisms and many viruses...

 from transcribing

Transcription (genetics)

Transcription is the process of creating a complementary RNA copy of a sequence of DNA. Both RNA and DNA are nucleic acids, which use base pairs of nucleotides as a complementary language that can be converted back and forth from DNA to RNA by the action of the correct enzymes...

 RNA. Inducer

Inducer

In molecular biology, an inducer is a molecule that starts gene expression.For a gene to be expressed, its DNA sequence must be copied to make a smaller, mobile molecule called messenger RNA , which carries the instructions for making a protein to the site where the protein is manufactured...

s cause repressor proteins to change shape

Conformational change

A macromolecule is usually flexible and dynamic. It can change its shape in response to changes in its environment or other factors; each possible shape is called a conformation, and a transition between them is called a conformational change...

 or otherwise become unable to bind DNA

DNA

Deoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms . The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in...

, allowing RNA polymerase to continue transcription.

Other regulatory genes code for activator proteins. An activator binds to a site on the DNA molecule and causes an increase in transcription of a nearby gene. In prokaryotes, a well-known example of an activator protein is the catabolite activator protein

Catabolite Activator Protein

Catabolite Activator Protein or CAP is a transcriptional activator that exists as a homodimer in solution, with each subunit comprising a ligand-binding domain at the N-terminus , which is also responsible for the dimerization of the protein, and a DNA-binding domain at the C-terminus...

 or CAP, which is involved in positive control

Positive control

Positive control may refer to:* Positive control group in scientific control* Positive control, the Air traffic control practice of controlling aircraft whose positions are determined by direct radar observation...

 of the lac operon

Lac operon

The lac operon is an operon required for the transport and metabolism of lactose in Escherichia coli and some other enteric bacteria. It consists of three adjacent structural genes, lacZ, lacY and lacA. The lac operon is regulated by several factors including the availability of glucose and of...

.

In the regulation of gene expression

Regulation of gene expression

Gene modulation redirects here. For information on therapeutic regulation of gene expression, see therapeutic gene modulation.Regulation of gene expression includes the processes that cells and viruses use to regulate the way that the information in genes is turned into gene products...

, both activators and repressors are known to play important roles.