Insertion sequence
Encyclopedia
An insertion sequence is a short DNA
sequence that acts as a simple transposable element
. 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, which also carry accessory genes such as antibiotic 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 repeat
s. For example, the well-known IS911 (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). http://www-is.biotoul.fr/is/IS_infos/IS3_family.html#IS911
A particular insertion sequence may be named according to the form ISn, where n is a number
(e.g. IS1, IS2, IS3, IS10, IS50, IS911, IS26 etc.); this is not the only naming scheme used, however. Although insertion sequences are usually discussed in the context of prokaryotic
genome
s, certain eukaryotic
DNA sequences belonging to the family of Tc1/mariner transposable elements may be considered to be, insertion sequences. http://mmbr.asm.org/cgi/content/full/62/3/725#SEC6
In addition to occurring autonomously, insertion sequences may also occur as parts of composite transposon
s; in a composite transposon, two insertion sequences flank one or more accessory genes, such as an antibiotic resistance gene (e.g. Tn10
, Tn5). Nevertheless, there exist another sort of transposons, called unit transposons, that do not carry insertion sequences at their extremities (e.g. Tn7).
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.
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...
sequence that acts as a simple transposable element
Transposon
Transposable elements are sequences of DNA that can move or transpose themselves to new positions within the genome of a single cell. The mechanism of transposition can be either "copy and paste" or "cut and paste". Transposition can create phenotypically significant mutations and alter the cell's...
. Insertion sequences have two major characteristics: they are small relative to other transposable elements (generally around 700 to 2500 bp
Base pair
In molecular biology and genetics, the linking between two nitrogenous bases on opposite complementary DNA or certain types of RNA strands that are connected via hydrogen bonds is called a base pair...
in length) and only code for proteins implicated in the transposition
Transposition
Transposition may refer to:Mathematics* Transposition , a permutation which exchanges two elements and keeps all others fixed* Transposition, producing the transpose of a matrix AT, which is computed by swapping columns for rows in the matrix AGames* Transposition , different moves or a different...
activity (they are thus different from other transposons, which also carry accessory genes such as antibiotic resistance genes). These proteins are usually the transposase
Transposase
Transposase is an enzyme that binds to the ends of a transposon and catalyzes the movement of the transposon to another part of the genome by a cut and paste mechanism or a replicative transposition mechanism....
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 repeat
Inverted repeat
An inverted repeat is a sequence of nucleotides that is the reversed complement of another sequence further downstream.For example, 5'---GACTGC....GCAGTC---3'. When no nucleotides intervene between the sequence and its downstream complement, it is called a palindrome. Inverted repeats define the...
s. For example, the well-known IS911 (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). http://www-is.biotoul.fr/is/IS_infos/IS3_family.html#IS911
A particular insertion sequence may be named according to the form ISn, where n is a number
Natural number
In mathematics, the natural numbers are the ordinary whole numbers used for counting and ordering . These purposes are related to the linguistic notions of cardinal and ordinal numbers, respectively...
(e.g. IS1, IS2, IS3, IS10, IS50, IS911, IS26 etc.); this is not the only naming scheme used, however. Although insertion sequences are usually discussed in the context of prokaryotic
Prokaryote
The prokaryotes are a group of organisms that lack a cell nucleus , or any other membrane-bound organelles. The organisms that have a cell nucleus are called eukaryotes. Most prokaryotes are unicellular, but a few such as myxobacteria have multicellular stages in their life cycles...
genome
Genome
In modern molecular biology and genetics, the genome is the entirety of an organism's hereditary information. It is encoded either in DNA or, for many types of virus, in RNA. The genome includes both the genes and the non-coding sequences of the DNA/RNA....
s, certain eukaryotic
Eukaryote
A eukaryote is an organism whose cells contain complex structures enclosed within membranes. Eukaryotes may more formally be referred to as the taxon Eukarya or Eukaryota. The defining membrane-bound structure that sets eukaryotic cells apart from prokaryotic cells is the nucleus, or nuclear...
DNA sequences belonging to the family of Tc1/mariner transposable elements may be considered to be, insertion sequences. http://mmbr.asm.org/cgi/content/full/62/3/725#SEC6
Transposon
Transposable elements are sequences of DNA that can move or transpose themselves to new positions within the genome of a single cell. The mechanism of transposition can be either "copy and paste" or "cut and paste". Transposition can create phenotypically significant mutations and alter the cell's...
s; in a composite transposon, two insertion sequences flank one or more accessory genes, such as an antibiotic resistance gene (e.g. Tn10
Tn10
Tn 10 is a transposable element, which is a sequence of DNA that is capable of mediating its own movement through the DNA of host organisms. This fragment of DNA can move from position to position on the chromosome or plasmid by cut-and-paste transposition...
, Tn5). Nevertheless, there exist another sort of transposons, called unit transposons, that do not carry insertion sequences at their extremities (e.g. Tn7).
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.