The genome of Yersinia pestis, the causative agent of plague, contains at least 30 copies of an element, designated IS1541, which is structurally related to IS200(85% identity). One such element is inserted within the chromosomalinv gene (M. Simonet, B. Riot, N. Fortineau, and P. Berche, Infect. Immun. 64:375–379, 1996). We characterized other IS1541 insertions by cloning 14 different Y. pestis 6/69M loci carrying a single copy of this insertion sequence (IS) into Escherichia coli and, for each element, sequencing 250 bp of both flanking regions. In no case was this IS element inserted into large open reading frames; however, in eight cases, it was detected downstream (17 to 139 bp) of genes thought to be transcribed monocistronically or which constituted the last gene of an operon, and in only one case was it detected upstream (37 bp) of the first gene of an operon. Sequence analysis revealed stem-loop structures (ΔG, <−10 kcal) resembling rho-independent transcription terminators in 8 of the 14 insertion sites. These motifs might constitute hot spots for insertion of this IS1541element within the Y. pestis genome.
The IS200-like insertion sequence (IS) is a 708-bp element recently found in Yersinia pestis. Its nucleotide sequence is 85% identical to that of IS200 recovered in most Salmonella enterica isolates. It is also present in multiple copies in Y. pseudotuberculosis. In contrast, this IS is found in some (biotype 1B strains) but not other Y. enterocolitica strains and is absent in the nonpathogenic yersiniae: Y. frederiksenii, Y. kristensenii, Y. intermedia, Y. bercovieri, and Y. mollaretii. The number and locations of the ISs in the Y. pseudotuberculosis genome vary among strains, resulting in a high degree of polymorphism, but IS fingerprints are stable after multiple subcultures of clinical isolates. The discriminative power of IS typing is better than that of ribotyping and almost as good as that of the time-consuming method of pulsotyping. Overall, IS200-like is a useful molecular marker in determining the epidemiology of Y. pseudotuberculosis infections.
We characterized Yersinia enterocolitica and Yersinia pseudotuberculosis insertion sequences related to insertion sequence 1541, recently identified in Yersinia pestis. For each of the two species, two insertion sequence copies were cloned and sequenced. Genetic elements from Y. pseudotuberculosis were almost identical to insertion sequence 1541, whereas these from Y. enterocolitica were less related. Phylogenetic analysis of the putative transposases encoded by insertion sequences from the three pathogenic members of the genus Yersinia showed that they clustered with those encoded by Escherichia coli and Salmonella enterica elements belonging to the insertion sequence 200/insertion sequence 605 group. Insertion sequences originating from Y. pestis and Y. pseudotuberculosis constitute a monophyletic lineage distinct from that of Y. enterocolitica.
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