Episome

episome

[′ep·ə‚sōm]

(genetics)

A circular genetic element in bacteria, presumably a deoxyribonucleic acid fragment, which is not necessary for survival of the organism and which can be integrated in the bacterial chromosome or remain free.

McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.

The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Episome

 

a genetic factor that can exist in a cell either autonomously (in the cytoplasm) or integrated with the chromosome; a molecule of deoxyribonucleic acid. The genome of the temperate lambda bacteriophage, the sex (or F) factor, and some R factors that transmit drug resistance to bacteria, for example, are episomes.

Episomes are not essential constituents of cells, and they can change from one state to another, depending on the type of cell. In E. coli cells, for example, the genome of the temperate lambda bacteriophage may be either integrated or autonomous, whereas in the cells of the causative agent of typhoid fever it is found only in the autonomous state. Most autonomous episomes behave like typical plasmids. Some researchers regard episomes as a transitional link between the structures that determine chromosomal and nonchromosomal heredity.

REFERENCES

Stent, G. Molekuliarnaia genetika. Moscow, 1974. (Translated from English.)
Meynell, G. Bakterial’nve plazmidy. Moscow, 1976. (Translated from English.) ’

V. G. LIKHODED

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.