Characterisation of IS1126 from Porphyromonas gingivalis W83: a new member of the IS4 family of insertion sequence elements.

The nucleotide sequence of IS1126, the only insertion sequence so far isolated from the oral pathogen Porphyromonas gingivalis, has been determined. It had a nucleotide sequence of 1338 base pair (bp) flanked by 12 bp perfect inverted repeats and generated a 5 bp target site duplication. The single major open reading frame encoded a predicted protein of 361 amino acids and molecular mass of 41 kDa. The gene encoding the transposase was subcloned into pUC18 and the transposase expressed in Escherichia coli minicells. The predicted amino acid sequence of the transposase had homology to putative transposases of IS1106 and IS1186 both of which belong to the IS5 group within the IS4 super-family of insertion elements. On the basis of this homology we propose that IS1126 should also be included in the IS5 group. Southern-blot analysis of a number of P. gingivalis strains using IS1126 as a probe revealed a unique pattern of hybridisation for each strain and the absence of IS1126 from other closely related Porphyromonas species. This should allow IS1126 to be used as a rapid epidemiological tool in studying oral infections by P. gingivalis.