Fis plays a role in Tn5 and IS50 transposition

Abstract

The Fis (factor for inversion stimulation) protein of Escherichia coli was found to influence the frequency of transposon TnS and insertion sequence ISSO transposition. Fis stimulated both TnS and IS50 transposition events and also inhibited IS50 transposition in Dam-bacteria. This influence was not due to regulation by Fis of the expression of the TnS transposition proteins. We localized, by DNase I footprinting, one Fis site overlapping the inside end of IS50 and give evidence to strongly suggest that when Fis binds to this site, IS50 transposition is inhibited. The Fis site at the inside end overlaps three Dam GATC sites, and Fis bound efficiently only to the unmethylated substrate. Using a mobility shift assay, we also identified another potential Fis site within IS50.Given the growth phase-dependent expression of Fis and its differential effect on Tn5 versus IS50 transposition in Dam-bacteria, we propose that the high levels of Fis present during exponential growth stimulate transposition events and might bias those events toward Tn5 and away from IS50 transposition.TnS is a composite prokaryotic transposon which was originally isolated from a Kiebsiella R-factor (3), although it functions in a wide variety of gram-negative bacteria. It is composed of two insertion sequence IS50 elements oriented as inverted repeats with respect to a unique region encoding resistance to several antibiotics (Fig. 1). In general, transposition requires four components: (i) the element-encoded protein(s), termed transposase(s), which catalyze the DNA strand transfer reactions; (ii) specific DNA sequences at the ends of the transposon which delimit the element; (iii) accessory host factors which stimulate the reaction, most probably by facilitating the formation of higher-order protein-nucleic acid complexes; and (iv) target DNA (see reference 6 for a general review of transposition). Most prokaryotic transposons transpose to various target DNA sites with little sequence specificity. So, although transposition does require specific sequences at the ends of the element, it does not require homology with transposon sequences at the target site. Transposition therefore represents a distinct class of DNA rearrangements from the site-specific recombination reactions, in which reciprocal DNA strand exchange occurs between two precisely defined and closely related DNA sites. We are interested both in studying the regulation of TnS transposition in Escherichia coli and also in analyzing the mechanism of transposition utilized by TnS.TnS transposition requires the element-encoded transposase (Tnp) (13,20) Fis (factor for inversion stimulation) is a small, heat-stable DNA-binding protein in E. coli which was originally discovered through its ability to stimulate several site-specific DNA inversion reactions (18,22). Fis binds to its target site as a 20-kDa dimer and induces a substantial bend (>900) in the DNA (38), a property which is probably important in its various functions. In addition to its role in the DNA inversion systems, Fis...

Sequence, regulation, and functions of fis in Salmonella typhimurium

“…Increased stability of and Mu lysogens is also observed in the presence of Fis (3,5,6). Even transposition frequencies of transposon Tn5 and insertion sequence IS50 are found to be influenced by Fis (60).…”

Epigenetic Gene Regulation in the Bacterial World

“…Thus, immediately following DNA replication, Fis binds to the IE, inhibiting IS50 transposition, and counteracts the positive effects of the hemimethylated state on IS50 transposition. In contrast, Tn5 transposition is not inhibited by Fis, since it does not use IE (276).…”

“…Increased transposition of IS50 and Tn5 in a Dam Ϫ host requires integration host factor (IHF), probably to compensate for a DNA conformational defect associated with the lack of Dam (165). In turn, binding of Fis (factor for inversion stimulation) to the IE inhibits IS50 transposition (276). Methylation of three GATC sites within the Fis recognition sequence inhibits Fis binding.…”

Transposons Tn 10 and Tn 5

“…For example, the expression of both transposase proteins is downregulated by Dam methylation of promoter elements in the respective transposase genes (18,19). IHF and Fis (factor for inversion stimulation) have also been identified as regulators of Tn5 transposition, although with the exception of the action of IHF in the Tn10 system, the mechanisms of action for the other factors have not been well defined (20,21,22). In addition there is evidence that the transcriptional repressor LexA can repress Tn5 transposase gene transcription (23).…”