Insertion sequence

An Insertion Sequence (also known as an IS, an insertion sequence element, an IS element) is a short DNA sequence that acts as a simple transposable element. Insertion Sequences have two major characteristics: they are relatively small related to others transposable elements (generally around 700 to 2500 bp in length) and only code for proteins implicated in the transposition activity. 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 IS911 (1250 bp) is flanked by two 36bp inverted repeat extremities and the coding region has 2 genes partially overlapping OrfA and OrfAB, coding the transposase (OrfAB) and a regulatory protein (OrfA). [1] 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, etc.); this is not the only naming scheme used, however. Although insertion sequences are usually discussed in the context of prokaryotic genomes, certain eukaryotic DNA sequences, belonging to the familly of TC1/Mariner transposable element may be considered to be insertion sequences. [2]

In addition to occurring autonomously, insertion sequences may also occur as parts of composite transposons; in a composite transposon (also known as a "complex transposon" or sometimes simply referred to as a "transposon"), two insertion sequences flank one or more accessory genes, such as antibiotic resistance gene.

See also

• Mobile genetic elements

References

• Campbell, Neil A. and Reece, Jane B. (2002). Biology (6th ed.), pp. 345-346. San Francisco: Benjamin Cummings. ISBN 0-8053-6624-5.
• Mahillon, Jacques and Chandler, Michael (1998). "Insertion sequences". Microbiology and Molecular Biology Reviews 62 (3), 725-774. Retrieved January 11, 2006.
• Prescott, Lansing M.; Harley, John P.; and Klein, Donald A. (2002). Microbiology (5th ed.), pp. 298-299. New York: McGraw-Hill. ISBN 0-07-232041-9.
• Shuler, Michael L. and Kargi, Fikret (2002). Bioprocess Engineering: Basic Concepts (2nd ed.), p. 220. Upper Saddle River, NJ: Prentice Hall PTR. ISBN 0-13-081908-5.

External link

• IS Finder