Conjugative transposons

Conjugative transposons are self-transmissible large DNA elements (up to 150kbp) located in the donor chromosome. After excision a circular intermediate is formed that is unable to replicate autonomously. It is nicked at a origin of transfer site and one strand is then transferred to the recipient cell. After generating a double-stranded circle the transposon integrates into the recipients chromosome. 

Resistance can emerge by mutation, though more commonly it is due to plasmid-encoded trimethoprim-resistant dihydrofolate reductases. These resistant enzymes may be located within transposons on conjugative plasmids that exhibit a broad host range, accounting for rapid and widespread dissemination of trimethoprim resistance among numerous bacterial species. 

AA Salyers, NB Shoemaker, AM Stevens, LY Li. Conjugative transposons an unusual and diverse set of integrated gene transfer elements. Microbiol Rev 59 579-590, 1995. 

Inducible resistance to high levels of vancomycin in enterococci is mediated by transposon Tn 1546 or related transposons [262, 263]. The transposition of Tn 1546 into plasmids with a broad host range or into con-jugative transposons would enable resistance to spread to 5. aureus which can exchange genetic information with enterococci [260]. Plasmid-mediated resistance to vancomycin has been successfully conjugated, in laboratory experiments, from enterococci to S. aureus, provided that erythromycin (6) and not vancomycin was used as the selective agent [265], It was only a question of time before such an event was shown to occur clinically [266, 267] and vancomycin resistance has now been found in an MRSA strain [268]. The seriousness of this cannot be over-emphasized. 

Perreten, V., Kolloffel, B., and Teuber, M. 1997. Conjugal transfer of the Tn916-like transposon TnFOl from Enterococcus faecalis isolated from cheese to other Gram-positive bacteria. Syst. Appl. Microbiol. 20, 27-38. 

S. aureus transposons are small mobile elements that often encode resistance genes (P-lactamase, resistance to erythromycin and tetracycline). All the transposons encode a transposase gene, and the product of this gene catalyses excision and/or replication of the element, as well as integration. Horizontal transfer of transposons to other S. aureus cells is presumably mediated by another MGE that is transferred, most likely a plasmid transferred by transduction or conjugation. Conjugative transposons have also been described in S. aureus. However, it is not clear if native conjugative transposons are found in S. aureus (Novick 1990). 

Clewell, D.B., Flannagan, S.E., and Jaworski, D.D. 1995, Unconstrained bacterial promiscuity the Tn916-Tnl545 family of conjugative transposons. Trends Microbiol 3 229-236. 

Trieu-Cuot, P., Poyart-Salmeron, C., Carlier, C., and Courvalin, P. 1990, Nucleotide sequence of the erythromycin resistance gene of the conjugative transposon Tnl545. Nucleic Acids Res 18 3660... 

A genetic linkage between nisin production, nisin immunity and the ability to use sucrose as a carbon source, was corroborated by the observation that these properties were transferred in a conjugation-like process [94]. It appeared that nisin and sucrose genes were clustered on chromosomal elements that were conjugative transposons [32,37,95,96]. 

The best characterized conjugative sucrose-nisin transposons are the 70-kb Tn5276 and Tn5301 [95, 97]. The conjugative transposon Tn5276 and Tn5301... 

Horn N, Swindell S, Dodd H, Gasson M (1991) Nisin biosynthesis genes are encoded by a novel conjugative transposon. Mol Gen Genet 228 129-135... 

Rauch PJG, De Vos WM (1992) Characterization of the novel nisin-sucrose conjugative transposon Tn5276 and its insertion in Lactococcus lactis. J Bacteriol 174 1280-1287... 

Rauch PJG, De Vos WM (1994) Identification and characterization of the genes involved in excision of the Lactococcus lactis conjugative transposon Tn5276. J Bacteriol 176 2165-2171... 

Poyart-Salmeron C, Trieu-Cuot P, Carlier C, Comvalin P (1989) Molecular characterization of two proteins involved in the excision of the conjugative transposon Tnl545 homologies with other site-specific recombinases. EMBO J 8 2425-2433... 

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