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A chimeric ribozyme in clostridium difficile combines features of group I introns and insertion elements
1Verfügungsgebäude für Forschung und Entwicklung, Institut für Medizinische Mikrobiologie und Hygiene, Johannes Gutenberg-Universität, Mainz, Germany.
Molecular Microbiology
|August 10, 2000
Summary
CdlSt1, a mobile DNA insertion in Clostridium difficile, combines group I intron and IS605-like element features. This element is widespread and precisely spliced, rendering its transposition harmless to the interrupted gene.
Area of Science:
- Molecular Biology
- Microbiology
- Genetics
Background:
- Clostridium difficile is a significant cause of infectious diarrhea.
- The enterotoxin gene tcdA plays a crucial role in C. difficile pathogenicity.
- Genetic elements within bacterial pathogens can influence virulence and transmission.
Purpose of the Study:
- To characterize the novel DNA insertion element CdlSt1 found within the C. difficile tcdA gene.
- To investigate the structure, splicing, and distribution of CdlSt1 in C. difficile strains.
- To understand the functional implications of CdlSt1 integration on the tcdA gene and toxin production.
Main Methods:
- Identification and sequencing of the CdlSt1 element within the tcdA-C34 gene.
- Analysis of CdlSt1's genetic structure, including intron and insertion sequence-like features.
- Experimental verification of CdlSt1 splicing from primary transcripts and assessment of TcdA toxin activity.
- Bioinformatic searches for CdlSt1-related sequences across diverse C. difficile strains.
Main Results:
- CdlSt1 is a 1975 bp DNA insertion element with a composite structure, incorporating group I intron features and an IS605-like insertion sequence.
- CdlSt1 is accurately spliced from tcdA-C34 primary transcripts, and purified TcdA toxin retains normal size and catalytic activity.
- CdlSt1-related sequences are widespread in both toxinogenic and non-toxinogenic C. difficile strains, indicating its mobility.
- Ten homologous CdlSt1 variants were identified in strain C34, integrated into open reading frames and precisely spliced.
Conclusions:
- CdlSt1 represents a mobile genetic element with a unique chimeric structure, combining invasiveness with precise splicing capabilities.
- The splicing mechanism of CdlSt1 renders its transposition harmless to the interrupted tcdA gene, suggesting a mechanism for maintaining gene integrity.
- The widespread distribution of CdlSt1 highlights its evolutionary significance and potential role in the genetic dynamics of Clostridium difficile.