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TopicPage for IS Elements of Escherichia coli K-12

Horizontal Gene Transfer

Description:

Insertion sequence (IS) elements are DNA sequences that are capable of independent transposition. The mechanism of transposition is usually replicative producing IS copies elsewhere in the genome.

The IS elements are grouped into families based on the similarities of their gene products and DNA sequence organization, such as the IS3 family that includes a diverse set of IS elements.

Specific instances of IS element types, e.g IS1A or IS5B, can be identical copies, nearly identical isotypes, or partial sequences.

The authoritative IS database IS Finder contains IS sequences from many bacteria and archaea, and is a registry for new IS sequence nomenclature and a repository for IS sequences at the CNRS, France, with web-based analytical tools. (Siguier, 2006). IS Finder also has a comprehensive online review of IS sequence and function.

Details:

Transposition is facilitated by IS-encoded transposases, often subject to programmed translational frameshifting. Many IS elements have small terminal inverted repeats (IR) that can be the targets of transposase action. Many of the E. coli K-12 IS elements are active and mutagenic.

Insertion mutations interrupting gene function can accumulate in response to natural evolutionary pressure, laboratory domestication, or experimental mutant hunts using various selections or screens.

The 44 IS elements of E. coli include several different types of IS elements including

IS1(7), IS2(7), IS3(5), IS4(1), IS5(11), IS30(4), IS150(1), IS186(3), IS609(1), IS911'(2).

There is also a partially deleted IS600' and two partial IS elements, the IS3-like ISX' and the IS4-like ISZ', that is closely related to ISEhe3 (Rudd, 1998).