Distribution of IS91 family insertion sequences in bacterial genomes: evolutionary implications.
ABSTRACT IS91 is the prototype element of a family of bacterial insertion sequences that transpose by a rolling-circle mechanism. Although previously considered a rarity among IS elements, many new examples have been identified by sequence analysis of bacterial genomes. In this work we provide a summary of occurrences of IS91-like sequences in the GenBank database, characterise the genetic organisation of adjacent sequences, and analyse IS91 ecological significance under the light of current transposition mechanisms. Interestingly, IS91 family elements were usually found adjacent to pathogenicity- and virulence-related genes. Thus, this might constitute the niche for IS91 and IS91 family elements to play an important role in the dissemination and evolution of virulence and pathogenicity types of genes.
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ABSTRACT: O antigen is part of the lipopolysaccharide present in the outer membrane of gram-negative bacteria. The surface-exposed O antigen is subject to selection by the host immune system, which may account for the maintenance of many different O-antigen forms. Characteristically, all genes specific to O-antigen synthesis are clustered in a region close to the his and gnd genes on the chromosome of Escherichia coli and related species. Shigella sonnei, essentially a clone of E. coli (E. coli clone Sonnei), is an important human pathogen and is unusual in that its O-antigen gene cluster is located on a plasmid. Our results suggest that it once had a normal chromosomal O-antigen gene cluster which has been largely deleted. We suggest that the O antigen encoded by the plasmid-borne genes offered a selective advantage in adapting to a new environment and that the chromosomal O-antigen genes were eventually inactivated. We also identified, by PCR and sequencing, a potential ancestor of E. coli Sonnei among the 166 known E. coli serotype strains.Journal of Bacteriology 07/1998; 180(11):2983-6. · 3.19 Impact Factor
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ABSTRACT: A transposable element, designated IS801, was isolated from strain LR781 of Pseudomonas syringae pathovar phaseolicola in two independent events using the entrapment plasmid, pUCD800. IS801 is 1517 base pairs in length and contains open reading frames that potentially encode proteins of 311 and 172 amino acids, as well as smaller proteins. Unlike most other prokaryotic transposable elements, IS801 lacks terminal repeats. Sequence analysis revealed two target pentamers for IS801 insertion that differ by one base pair. One copy of IS801 generated a perfect duplication of its target, TGAAC. The second copy of IS801 was flanked by the target, TGGAC, at one end, and TGAAC at the other end. A third copy of IS801 was cloned from pMMC7105, an indigenous plasmid of strain LR781, and it was flanked by copies of the pentamer TGAAC.Molecular Microbiology 04/1991; 5(3):617-22. · 4.96 Impact Factor
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ABSTRACT: The complete nucleotide sequence of the 4746bp HindIII fragment encoding the genes for the biosynthesis and assembly of CS3 pili has been determined. By site-directed mutagenesis in conjunction with analysis of the plasmid-encoded proteins in minicells, the actual reading frames for the various products have been determined. This demonstrated that the genes for four of the proteins (63 kD, 48 kD, 33 kD, and 20 kD in size) are encoded entirely within the same open reading frame as a fifth protein (104 kD). However, for synthesis of this latter protein, suppression or readthrough of an internal amber codon is required. Termination at this codon is also necessary for synthesis of the former proteins. Two further proteins are also encoded within the HindIII fragment: a 27 kD precursor of a periplasmic protein and the 17.5kD precursor of the major CS3 fimbrial subunit.Molecular Microbiology 01/1990; 3(12):1685-95. · 4.96 Impact Factor