An insertion sequence (IS) element of named was isolated and its complete nucleotide sequence determined. is 836 bp in length and occurs 20-35 times in the genome and 5-15 times in other species. Analysis of the junctions at the sites of insertion revealed a small target site duplication of four bases and inverted repeats of 17 bp with one mismatch. presents significant similarity (53.4%) with IS427 identified in suggesting a common ancestral sequence. A long ORF of 708 bp was identified encoding a protein with a predicted molecular mass of 26 kDa and sharing sequence identity with the hypothetical protein 1 of and with the transposase of is present in all strains we have tested. Restriction fragment length polymorphism of reference and field strains of two species and was studied using either pulsed field gel electrophoresis (PFGE) on -digested DNA or hybridization of RI-digested DNA using as a probe. The genome of biovar 3 contains about 10 IS copies per genome and field strains of the same species could not be distinguished either by IS hybridization or by I (PFGE) restriction patterns. In contrast, the number of IS copies in the genome is around 30 and the different field strains can be differentiated by both methods. As ISs have been shown to be implicated in chromosomal rearrangement, we propose that the chromosomal polymorphism revealed by PFGE and high copy number of observed in may be related to the presence of an active IS in this species.


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