Target specificity of insertion element IS30

Abstract

SummaryThe Escherichia coli resident mobile element IS30 has pronounced target specificity. Upon transposition, the element frequently inserts exactly into the same position of a preferred target sequence. Insertion sites in phages, plasmids and in the genome of E. coli are characterized by an exceptionally long palindromic consensus sequence that provides strong specificity for IS30 insertions, despite a relatively high level of degeneracy. This 24-bp-long region alone determines the attractiveness of the target DNA and the exact position of IS30 insertion. The divergence of a target site from the consensus and the occurrence of 'nonpermitted' bases in certain positions influence the target activity. Differences in attractiveness are emphasized if two targets are present in the same replicon, as was demonstrated by quantitative analysis. In a system of competitive targets, the oligonucleotide sequence representing the consensus of genomic IS30 insertion sites proved to be the most efficient target. Having compared the known insertion sites, we suppose that IS30-like target specificity, which may represent an alternative strategy in target selection among mobile elements, is characteristic of the insertion sequences IS3, IS6 and IS21, too.

Detection and analysis of transpositionally active head-to-tail dimers in three additional Escherichia coli IS elements

“…This cleavage site in the cases of IS30 (Olasz et al, 1997(Olasz et al, , 1998 and IS911 (Ton-Hoang et al, 1998;Turlan et al, 2000) proved to be at the same distance from the end of IRs both in dimerization or integration into the target site, resulting in the same length of the spacer and of the target duplication. On the other hand, the spacer in (IS2) 2 (Szeverényi et al, 1996a) and in (IS21) 2 (Reimmann & Haas, 1987) does not correspond to the target duplication characteristic for these elements.…”

Site-specific recombination by the DDE family member mobile element IS30transposase

“…This finding supports that mechanistically dissimilar enzymes can perform similar biological functions and suggests that transposition and site-specific recombination may be closer to each other in some respect than was supposed earlier. Further support for this idea may emerge from insertion sequence (IS) elements that form an active junction composed of the inverted repeats (IRs) (7)(8)(9)(10). This IR-IR junction shows similarities in its structure and function to the recombination sites of sitespecific systems.…”

“…The Escherichia coli element, IS30, encoding a Tpase with the well conserved DDE signature (11), belongs to the increasing class of elements that transpose through an intermediate formed by abutted IRs (8). The IR-IR joint bracketing a 2-bp spacer is composed of the 26-bp left and right IR ends (IRL and IRR, respectively) that differ at three positions (12).…”

“…The IR-IR joint bracketing a 2-bp spacer is composed of the 26-bp left and right IR ends (IRL and IRR, respectively) that differ at three positions (12). IR-IR joints occur in both IS dimers and minicircles that can integrate into hot spot sequences or next to other IS30 ends (13)(14)(15). Whereas transposition into a hot spot is a conventional way of translocation, which accompanies the resolution of IR-IR junction, targeting an IR end seems more specific for IS30 and generates a new IR-IR joint.…”

“…Whereas transposition into a hot spot is a conventional way of translocation, which accompanies the resolution of IR-IR junction, targeting an IR end seems more specific for IS30 and generates a new IR-IR joint. The IRs, together with the adjacent IS sequences, are important for the directionality of recombination, because, as always, IRL-IRR junction arises through dimerization or targeting an IR (8,13,16). The most frequent reaction has been observed when both donor and target DNA contain an IR-IR junction (13).…”