A genetic functional unit that controls production of a messenger RNA; it consists of an operator gene and two or more structural genes located in sequence in the cis position on one chromosome. [L. operor, to work, act, + -on]
- Lac o. a collection of adjacent bacterial genes responsible for the entry and metabolism of lactose; contains the genes coding for three enzymes and is flanked by a repressor and a promoter region to control expression.
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op·er·on 'äp-ə-.rän n a group of closely linked genes that produces a single messenger RNA molecule in transcription and that consists of structural genes and regulating elements (as an operator and promoter)
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n.
a group of closely linked genes that regulate the production of enzymes in bacteria. An operon is composed of one or more structural genes, which determine the nature of the enzymes made, and operator and promoter genes, which control the working of the structural genes. The operator is itself controlled by a regulator gene, which is not part of the operon.
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op·er·on (opґər-on) [L. opera work + Gr. -on neuter ending] in prokaryotes, a chromosomal segment constituting a functional unit of transcription and so of genetic regulation. It comprises one or more structural genes, their promoter, and an operator region that through interaction with a regulator protein controls the structural genes.
Escherichia coli lac operon. In the absence of lactose, the product of the repressor gene binds the operator region and prevents transcription of genes involved in lactose utilization by blocking movement of the RNA polymerase from promoter to structural gene region; the operon is repressed. If lactose is added, an inducer binds the repressor protein, lessening its affinity for the operator. The RNA polymerase can then proceed from promoter to structural genes, so that the operon is derepressed, or expressed.
Medical dictionary. 2011.