General features and properties of insertion sequence elements

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Transposase stability

Transposase stability can also contribute to control of transposition activity. The Tpase of IS903 is sensitive to the E. coli Lon protease (Derbyshire, et al., 1990). This sensitivity limits the activity of the Tpase both temporally and spatially and may provide an explanation for the observation that several Tpases function preferentially in cis. Indeed mutant IS903 Tpase derivatives have been isolated which exhibit an increased capacity to function in trans. These are more refractory to Lon degradation than the wildtype protein (Derbyshire & Grindley, 1996). Some evidence that Lon may also be involved in regulating Tn5 (IS50) transposition has also been presented (Krebs & Reznikoff, 1986).

An observation which might also reflect Tpase instability is the temperature sensitive nature of IS1-mediated adjacent deletions in vivo (Reif & Saedler, 1974), of Tn3 transposition (Kretschmer & Cohen, 1979) and of IS911 intramolecular recombination both in vivo and in vitro (Haren, et al., 1997). For IS911, incubation of the Tpase at 42ºC results in an irreversible loss in activity. Further analyses showed that there was an increase in the proportion of transposase fragments some of which can presumably interact with full length transposase to inhibit its activity. This effect can be somewhat reduced by a series of mutation in the transposase gene whose function in stabilising the transposase is as yet unknown (Gueguen, et al., 2006).

    References :
  • Derbyshire KM & Grindley ND (1996) Cis preference of the IS903 transposase is mediated by a combination of transposase instability and inefficient translation. Mol Microbiol 21: 1261-1272.
  • Derbyshire KM, Kramer M & Grindley ND (1990) Role of instability in the cis action of the insertion sequence IS903 transposase. Proc Natl Acad Sci U S A 87: 4048-4052.
  • Gueguen E, Rousseau P, Duval-Valentin G & Chandler M (2006) Truncated forms of IS911 transposase downregulate transposition. Mol Microbiol 62: 1102-1116.
  • Haren L, Betermier M, Polard P & Chandler M (1997) IS911-mediated intramolecular transposition is naturally temperature sensitive. Mol Microbiol 25: 531-540.
  • Krebs MP & Reznikoff WS (1986) Transcriptional and translational initiation sites of IS50. Control of transposase and inhibitor expression. J Mol.Biol. 192: 781-791.
  • Kretschmer PJ & Cohen SN (1979) Effect of temperature on translocation frequency of the Tn3 element. J.Bacteriol. 139: 515-519.
  • Reif HJ & Saedler H (1974) IS1 is Involved in Deletion Formation in the gal Region of E.coli K12. Mol.Gen.Genet. 137: 17-28.