A Chimeric Ribozyme in Clostridium Difficile Combines Features of Group I Introns and Insertion Elements

Mol Microbiol. 2000 Jun;36(6):1447-59. doi: 10.1046/j.1365-2958.2000.01965.x.


CdlSt1, a DNA insertion of 1975 bp, was identified within tcdA-C34, the enterotoxin gene of the Clostridium difficile isolate C34. Located in the catalytic domain A1-C34, Cd/St1 combines features of two genetic elements. Within the first 434 nt structures characteristic for group I introns were found; encoding the two transposase-like proteins tlpA and tlpB nucleotides 435-1975 represent the remainder of a IS605-like insertion element. We show that the entire CdlSt1 is accurately spliced from tcdA-C34 primary transcripts and that purified TcdA-C34 toxin is of regular size and catalytic activity. A search for CdlSt1-related sequences demonstrates that the element is widespread in toxinogenic and non-toxinogenic C. difficile strains, indicating the mobility of CdlSt1. In strain C34, we characterize 10 CdlSt1 variants; all are highly homologous to CdlSt1 (> 93% identity), integrated in bacterial open reading frames (ORFs), show the typical composite structure of CdlSt1 and are precisely spliced from their primary transcripts. CdlSt1-like chimeric ribozymes appear to combine the invasiveness of an insertion element with the splicing ability of a group I intron, rendering transposition harmless for the interrupted gene.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Bacterial Toxins / genetics
  • Base Sequence
  • Clostridium difficile / enzymology*
  • Clostridium difficile / genetics
  • DNA Transposable Elements*
  • Enterotoxins / genetics
  • Gene Expression Regulation, Bacterial
  • Genetic Variation
  • Introns*
  • Molecular Sequence Data
  • Nucleic Acid Conformation
  • RNA Splicing
  • RNA, Bacterial*
  • RNA, Catalytic*
  • Reverse Transcriptase Polymerase Chain Reaction


  • Bacterial Toxins
  • DNA Transposable Elements
  • Enterotoxins
  • RNA, Bacterial
  • RNA, Catalytic
  • tcdA protein, Clostridium difficile

Associated data

  • GENBANK/AJ131844