title: Genetics of type IIa heat-labile enterotoxin of Escherichia coli: operon fusions, nucleotide sequence, and hybridization studies.
abstract: Operon fusions for the Escherichia coli heat-labile enterotoxin type IIa (LT-IIa) operon were isolated and characterized. The LT-IIa genes are organized in a transcriptional unit similar to those of cholera toxin (CT) and the closely related E. coli heat-labile toxin type I (LT-I, with subtypes LTh-I and LTp-I). The nucleotide sequence of the LT-IIa genes was determined and compared with the sequences of LTh-I and CT. The A subunit gene of LT-IIa was found to be 57% homologous with the A subunit gene of LTh-I and 55% homologous with the A gene of CT. Most of the homology derived from the region of the A gene which encodes the A1 fragment. The B gene of LT-IIa was not homologous with the B gene of LTh-I or CT. DNA probes containing various portions of the LT-IIa genes and adjacent sequences were used for hybridization studies with restriction endonuclease fragments of DNA from a collection of LT-II-producing strains. These studies showed that a probe containing much of the A subunit gene hybridized well to DNA from the various strains, but a probe for the B subunit gene did not.
authors.affiliation: Department of Microbiology, Uniformed Services University of the Health Sciences, Bethesda, Maryland 20814-4799.
authors.forename: C L
authors.initials: CL
authors.lastname: Pickett
authors.forename: D L
authors.initials: DL
authors.lastname: Weinstein
authors.forename: R K
authors.initials: RK
authors.lastname: Holmes
mesh_terms: D000595:Amino Acid Sequence; D001427:Bacterial Toxins / Q000235:genetics*; D001483:Base Sequence; D003001:Cloning, Molecular; D004262:DNA Restriction Enzymes; D004768:Enterotoxins / Q000235:genetics*; D004926:Escherichia coli / Q000235:genetics*; D029968:Escherichia coli Proteins; D005796:Genes; D005798:Genes, Bacterial; D008969:Molecular Sequence Data; D009693:Nucleic Acid Hybridization; D009876:Operon
chemical_list: D001427:Bacterial Toxins; D004768:Enterotoxins; D029968:Escherichia coli Proteins; C027538:heat-labile enterotoxin, E coli; D004262:DNA Restriction Enzymes