title: Genetic characterization of Clostridium botulinum type A containing silent type B neurotoxin gene sequences.
abstract: A recent study detected genes encoding type B botulinum neurotoxin in some type A strains of Clostridium botulinum that exhibit no type B toxin activity. In this study, we investigated the presence, structure, linkage, and organization of genes encoding botulinum neurotoxin (BoNT) and other components of the progenitor complex. Sequence analysis showed that the silent BoNT/B gene is highly related to that from authentic proteolytic type B C. botulinum. However, a stop signal and deletions were found within the sequence. A non-toxin nonhemagglutinin gene (NTNH) was mapped immediately upstream of both the BoNT/A and silent BoNT/B genes. Significantly the NTNH gene adjacent to the defective BoNT/B gene was "chimeric, " the 5'- and 3'-regions of the gene had high homology with corresponding regions of the type B NTNH gene, while the 471-amino acid sequence in the central region was identical to NTNH of type A. Hemagglutinin genes HA-33 and HA-II were not found adjacent to the NTNH/A gene, but instead there was an unidentified open reading frame previously reported in strains of C. botulinum types E and F. By contrast HA-II, HA-33, and NTNH genes were located immediately upstream of the silent BoNT/B gene. Pulsed-field gel electrophoretic analysis of chromosomal DNA digests indicated the distance between type A and B gene clusters to be less than 40 kilobases.
authors.affiliation: Biological and Biotechnical Science Research Council, Institute of Food Research, Reading Laboratory, United Kingdom.
authors.forename: R A
authors.initials: RA
authors.lastname: Hutson
authors.forename: Y
authors.initials: Y
authors.lastname: Zhou
authors.forename: M D
authors.initials: MD
authors.lastname: Collins
authors.forename: E A
authors.initials: EA
authors.lastname: Johnson
authors.forename: C L
authors.initials: CL
authors.lastname: Hatheway
authors.forename: H
authors.initials: H
authors.lastname: Sugiyama
mesh_terms: D000595:Amino Acid Sequence; D001483:Base Sequence; D001905:Botulinum Toxins / Q000235:genetics*; D003014:Clostridium botulinum / Q000235:genetics*; D017931:DNA Primers; D015342:DNA Probes; D008969:Molecular Sequence Data; D005810:Multigene Family; D017386:Sequence Homology, Amino Acid
chemical_list: D017931:DNA Primers; D015342:DNA Probes; D001905:Botulinum Toxins