title: Insertional inactivation of an Escherichia coli urease gene by IS3411.
abstract: Ureolytic Escherichia coli are unusual clinical isolates that are found at various extraintestinal sites of infection, predominantly the urinary tract. The urease-positive phenotype is unstable in approximately 25% of these isolates, and urease-negative segregants are produced at a high frequency. We have studied the nature of the urease-positive-to-negative transition in one of these isolates, designated E. coli 1021. Southern hybridization experiments with genomic DNA extracted from seven independent E. coli 1021 urease-negative segregants revealed the presence of a 1.3-kb DNA insertion in the urease gene cluster. A DNA fragment containing the DNA insertion was cloned from one of the urease-negative segregants. This cloned DNA fragment was capable of mediating cointegrate formation with the conjugative plasmid pOX38, suggesting that the DNA insertion was a transposable element. The insert was identified as an IS3411 element in ureG by DNA sequence analysis. A 3-bp target duplication (CTG) flanking the insertion element was found. DNA spanning the insertion site was amplified from the other six urease-negative segregants by using the polymerase chain reaction. The DNA sequence of the amplified fragments indicated that an IS3411 element was found in an identical site in all urease-negative segregants examined. These data suggest that in E. coli 1021, IS3411 transposes at a high frequency into ureG at a CTG site, disrupting this gene and eliminating urease activity.
authors.affiliation: Department of Microbiology and Immunology, University of Miami School of Medicine, Florida 33101.
authors.forename: C M
authors.initials: CM
authors.lastname: Collins
authors.forename: D M
authors.initials: DM
authors.lastname: Gutman
mesh_terms: D001483:Base Sequence; D002874:Chromosome Mapping; D004251:DNA Transposable Elements / Q000235:genetics*; D004926:Escherichia coli / Q000235:genetics* / Q000472:pathogenicity; D008969:Molecular Sequence Data; D005810:Multigene Family / Q000235:genetics*; D016254:Mutagenesis, Insertional; D013329:Structure-Activity Relationship; D014510:Urease / Q000172:deficiency / Q000235:genetics*
chemical_list: D004251:DNA Transposable Elements; D014510:Urease