CLONING AND CHARACTERIZATION OF THE CYTOTOXIN L-ENCODING GENE OF CLOSTRIDIUM-SORDELLII - HOMOLOGY WITH CLOSTRIDIUM-DIFFICILE CYTOTOXIN-B

Hybridization of an oligodeoxyribonucleotide (oligo) probe, designed f rom a repeated sequence ('oligo rep') at the C terminus of the Clostri dium difficile (Cd) cytotoxin (Cyt), revealed that homologies exist be tween the Cd cyt gene and the genomes of several other clostridia, inc luding Clostridium sordellii (Cs), suggesting a common ancestral cyt a mongst the Clostridium genus. This Cd 'oligo rep' probe was used to cl one the Cs (strain 6018) cyt. The sequenced (7095 bp) region encodes 2 364 amino acids (aa) and corresponds to a protein of 270 614 Da, Cs Cy t has 76% identity with the Cd Cyt and 47% identity with the Cd entero toxin (Ent). The latter third of the protein consists of repeated unit s, similar to those found for Cd Cyt. A highly conserved hydrophobic d omain can be delineated. Few structural differences are evident betwee n Cd and Cs Cyt to explain their different cellular and sub-cellular e ffects. A small open reading frame (ORF) encoding a protein of 16484 D a is located 210 bp downstream from cyt. No homology was evident with any known sequence. The first 30 aa of this ORF may correspond to a si gnal peptide.