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(ĕp`ĭsōm), unit of genetic material composed of a series of genesgene,
the structural unit of inheritance in living organisms. A gene is, in essence, a segment of DNA that has a particular purpose, i.e., that codes for (contains the chemical information necessary for the creation of) a specific enzyme or other protein.
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 that sometimes has an independent existence in a host cell and at other times is integrated into a chromosomechromosome
, structural carrier of hereditary characteristics, found in the nucleus of every cell and so named for its readiness to absorb dyes. The term chromosome
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 of the cell, replicating itself along with the chromosome. Episomes have been studied in bacteria. One group of episomes are actually virusesvirus,
parasite with a noncellular structure composed mainly of nucleic acid within a protein coat. Most viruses are too small (100–2,000 Angstrom units) to be seen with the light microscope and thus must be studied by electron microscopes.
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 that infect bacteria. As autonomous units they destroy host cells, and as segments integrated into a chromosome they multiply in cell division and are transferred to daughter cells. Episomes called sex factors determine whether chromosome material will be transferred from one bacterium to another. Other episomes carry genes that make bacteria resistant to the inhibitory action of antibiotics. See recombinationrecombination,
process of "shuffling" of genes by which new combinations can be generated. In recombination through sexual reproduction, the offspring's complete set of genes differs from that of either parent, being rather a combination of genes from both parents.
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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.


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



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.
References in periodicals archive ?
have been developed as a part of episomal vector and suitability of these cell lines for in vitro screening of antileishmanial agents has been establised (52).
PEL cells may contain 50-150 copies/cell of episomal HHV8 genomes [102].
Intrinsic stability of episomal circles formed during human immunodeficiency virus type 1 replication.
Life Technologies is also introducing the Episomal iPSC Reprogramming Vectors, which leverages non-viral, non-integrating technology to deliver six genes to initiate the reprogramming of human somatic cells, such as blood and skin cells, to iPS cells.
Additionally, CDI's episomal reprogramming method is "footprint-free," meaning no foreign DNA is integrated into the genome of the reprogrammed cells, alleviating safety concerns over the possible use of iPS cells in therapeutic settings.
The new patent claims whole plants, root lines or plant cell lines harboring a self-replicating, episomal viral RNA vector encoding a gene of interest, and an Ri T-DNA or portion thereof sufficient to generate hairy roots.
Toward that end we developed the episomal reprogramming method to ensure that the resulting iPSCs are free of exogenous DNA, and this CIRM grant validates that method as researchers worldwide will access the resulting iPSC lines for disease research.
New World isolates have a distinct chromosomal translocation and an episomal variation in the open reading frame (ORF) 470 DNA sequence that distinguishes them from the other isolates tested.
In a study by Kaplan et al, (8) clonal analysis of specimens from 8 patients with PTLD--all classified as B-cell monomorphous, high-grade lymphomas--was performed using both episomal EBV and immunoglobulin genes as markers.
Since productive life cycle of HPV is tightly linked with the differentiation programme of infected epithelial cells, various leads are being tested for their activity at different stages of HPV's life cycle in the host cell which include virus binding and entry, presence of viral DNA in episomal form and its replication in host cells as well as host cell-dependent expression of viral oncogenes following integration of its DNA into the host cells.