Insertion element (also known as an IS, an insertion sequence element, or an IS element) is a short
DNA sequence that acts as a simple
transposable element
A transposable element (TE, transposon, or jumping gene) is a nucleic acid sequence in DNA that can change its position within a genome, sometimes creating or reversing mutations and altering the cell's genetic identity and genome size. Transp ...
. Insertion sequences have two major characteristics: they are small relative to other transposable elements (generally around 700 to 2500
bp in length) and only code for proteins implicated in the
transposition activity (they are thus different from other
transposons
A transposable element (TE, transposon, or jumping gene) is a nucleic acid sequence in DNA that can change its position within a genome, sometimes creating or reversing mutations and altering the cell's genetic identity and genome size. Transpo ...
, which also carry accessory genes such as
antibiotic resistance
Antimicrobial resistance (AMR) occurs when microbes evolve mechanisms that protect them from the effects of antimicrobials. All classes of microbes can evolve resistance. Fungi evolve antifungal resistance. Viruses evolve antiviral resistance. ...
genes). These proteins are usually the
transposase which catalyses the enzymatic reaction allowing the IS to move, and also one regulatory protein which either stimulates or inhibits the transposition activity. The coding region in an insertion sequence is usually flanked by
inverted repeats. For example, the well-known IS''911'' (1250 bp) is flanked by two 36bp inverted repeat extremities and the coding region has two genes partially overlapping ''orfA'' and ''orfAB'', coding the transposase (OrfAB) and a regulatory protein (OrfA). A particular insertion sequence may be named according to the form IS''n'', where ''n'' is a
number
A number is a mathematical object used to count, measure, and label. The original examples are the natural numbers 1, 2, 3, 4, and so forth. Numbers can be represented in language with number words. More universally, individual numbers c ...
(e.g. IS''1'', IS''2'', IS''3'', IS''10'', IS''50'', IS''911'', IS''26'' etc.); this is not the only naming scheme used, however. Although insertion sequences are usually discussed in the context of
prokaryotic genome
In the fields of molecular biology and genetics, a genome is all the genetic information of an organism. It consists of nucleotide sequences of DNA (or RNA in RNA viruses). The nuclear genome includes protein-coding genes and non-coding ge ...
s, certain
eukaryotic
Eukaryotes () are organisms whose cells have a nucleus. All animals, plants, fungi, and many unicellular organisms, are Eukaryotes. They belong to the group of organisms Eukaryota or Eukarya, which is one of the three domains of life. Bacte ...
DNA sequences belonging to the family of Tc1/''mariner'' transposable elements may be considered to be, insertion sequences.
In addition to occurring autonomously, insertion sequences may also occur as parts of
composite transposons; in a composite transposon, two insertion sequences flank one or more accessory genes, such as an antibiotic resistance gene (e.g.
Tn10 Tn''10'' is a transposable element, which is a sequence of DNA that is capable of mediating its own movement from one position in the DNA of the host organism to another. There are a number of different transposition mechanisms in nature, but Tn' ...
, Tn''5''). Nevertheless, there exist another sort of transposons, called unit transposons, that do not carry insertion sequences at their extremities (e.g. Tn''7'').
A complex transposon does not rely on flanking insertion sequences for resolvase. The resolvase is part of the tns genome and cuts at flanking inverted repeats.
Transposition frequency of IS elements is dependent of multiple parameters, including culture growth phase, medium composition, oxygen tension, growth scale, and structural conformation of target sites (e.g.: curvature, presence of certain motifs, DNA composition).
. Recombination between genomic IS sites can enable bacteria to adapt to new environments, making IS elements an important mechanism for evolution in bacteria.
See also
*
Mobile genetic elements
References
* Campbell, Neil A. and Reece, Jane B. (2002). ''Biology'' (6th ed.), pp. 345–346. San Francisco: Benjamin Cummings. .
*
* Prescott, Lansing M.; Harley, John P.; and Klein, Donald A. (2002). ''Microbiology'' (5th ed.), pp. 298–299. New York: McGraw-Hill. .
* Shuler, Michael L. and Kargi, Fikret (2002). ''Bioprocess Engineering: Basic Concepts'' (2nd ed.), p. 220. Upper Saddle River, NJ: Prentice Hall PTR. .
External links
IS Finder
{{Authority control
Molecular biology
Mobile genetic elements