title: Atypical association of DDE transposition with conjugation specifies a new family of mobile elements.
abstract: We describe in Streptococcus agalactiae an atypical family of conjugative transposons named TnGBSs which associates DDE transposition and conjugation. We present evidence that the transposition of TnGBS2, the prototype of this family, is catalysed by a new class of DDE transposases that are widespread in Gram-positive bacteria. Remarkably, transposition occurs in intergenic regions, 15 or 16 bp upstream the -35 sequence of promoters, minimizing the burden on the host cell and suggesting an association between transcription and transposition. Transposition catalyses the formation of a circular intermediate that is substrate for subsequent conjugative intercellular transfer. Conjugation is initiated at an origin of transfer by a transposon-encoded relaxase. Whereas all integrative and conjugative elements described so far encode a phage-related integrase, TnGBS2 is the first example of conjugative transposon whose recombination is mediated by a DDE transposase. The combination of DDE transposition with conjugation implies recombination constraints linked to the physical separation of donor and recipient molecules.
authors.affiliation: Institut Pasteur, Unité de Génétique des Génomes Bactériens, CNRS URA 2171, France.
authors.forename: Mathieu
authors.initials: M
authors.lastname: Brochet
authors.forename: Violette
authors.initials: V
authors.lastname: Da Cunha
authors.forename: Elisabeth
authors.initials: E
authors.lastname: Couvé
authors.forename: Christophe
authors.initials: C
authors.lastname: Rusniok
authors.forename: Patrick
authors.initials: P
authors.lastname: Trieu-Cuot
authors.forename: Philippe
authors.initials: P
authors.lastname: Glaser
mesh_terms: D000595:Amino Acid Sequence; D001483:Base Sequence; D003227:Conjugation, Genetic; D004251:DNA Transposable Elements; D004269:DNA, Bacterial / Q000235:genetics; D008969:Molecular Sequence Data; D016254:Mutagenesis, Insertional; D013292:Streptococcus agalactiae / Q000235:genetics*; D019895:Transposases / Q000235:genetics*
chemical_list: D004251:DNA Transposable Elements; D004269:DNA, Bacterial; D019895:Transposases