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.,
- 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:
- 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.