A chimeric ribozyme in clostridium difficile combines features of group I introns and insertion elements.
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.
Braun
V
V
Verfügungsgebäude für Forschung und Entwicklung, Institut für Medizinische Mikrobiologie und Hygiene, Johannes Gutenberg-Universität, Mainz, Germany.
Mehlig
M
M
Moos
M
M
Rupnik
M
M
Kalt
B
B
Mahony
D E
DE
von Eichel-Streiber
C
C
D000595:Amino Acid Sequence; D001427:Bacterial Toxins / Q000235:genetics; D001483:Base Sequence; D016360:Clostridioides difficile / Q000201:enzymology* / Q000235:genetics; D004251:DNA Transposable Elements; D004768:Enterotoxins / Q000235:genetics; D015964:Gene Expression Regulation, Bacterial; D014644:Genetic Variation; D007438:Introns; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation; D012326:RNA Splicing; D012329:RNA, Bacterial; D016337:RNA, Catalytic; D020133:Reverse Transcriptase Polymerase Chain Reaction
D001427:Bacterial Toxins; D004251:DNA Transposable Elements; D004768:Enterotoxins; D012329:RNA, Bacterial; D016337:RNA, Catalytic; C041348:tcdA protein, Clostridium difficile