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Chapter 25 : Tetracycline Regulation of Conjugal Transfer Genes

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Tetracycline Regulation of Conjugal Transfer Genes, Page 1 of 2

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Abstract:

This chapter focuses on tetracycline-responsive regulatory system of the conjugative transposons. If a strain carrying a conjugative transposon is exposed to tetracycline, the frequency with which the conjugative transposon is transferred increases by at least 1,000-fold. The conjugative transposons not only transfer themselves from a donor to a recipient cell but are also capable of mobilizing coresident plasmids and excising and mobilizing unlinked elements called nonreplicating bacteroides units (NBUs). Insertional disruption of or abolishes element self-transfer of the conjugative transposon, mobilization of coresident plasmids, and excision-circularization and mobilization of NBUs. Two obvious candidates for genes that might be controlled by RteC are the mobilization gene(s) of the conjugative transposon, which nick the element's own and initiate transfer, and the genes involved in excision. At first, RteC was assumed to be a transcriptional activator, although there was no evidence that RteC binds DNA nor was any DNA binding motif apparent in the deduced amino acid sequence of RteC. The regulatory machinery of the conjugative transposons is turning out to be much more complex than expected. It is important to bear in mind the fact that transfer of would not have been detected if tetracycline had not been incorporated in the medium used to grow the donors. Thus, some chromosomally encoded genes that appear to be nontransmissible could actually be carried on a conjugal element, whose transfer functions must be stimulated by some inducer not normally included in the medium.

Citation: Salyers A, Shoemaker N, Stevens A. 1995. Tetracycline Regulation of Conjugal Transfer Genes, p 393-400. In Hoch J, Silhavy T (ed), Two-Component Signal Transduction. ASM Press, Washington, DC. doi: 10.1128/9781555818319.ch25

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Figures

Image of FIGURE 1
FIGURE 1

Schematic diagram of location of transfer and regulatory genes on conjugative transposon, Tc Em DOT. Three regulatory genes (, , and ) are located near the center o f the 70-kbp element. The of the conjugative transposon is located downstream of . Adjacent to the oriT region is a 15-kbp region that contains all the genes necessary for transfer of the element. The mobilization gene(s) of Tc DOT, which nicks at to initiate the transfer process, is presumably located within this region but is indicated by (mob) because their precise location is not known.

Citation: Salyers A, Shoemaker N, Stevens A. 1995. Tetracycline Regulation of Conjugal Transfer Genes, p 393-400. In Hoch J, Silhavy T (ed), Two-Component Signal Transduction. ASM Press, Washington, DC. doi: 10.1128/9781555818319.ch25
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Image of FIGURE 2
FIGURE 2

Interaction o f NBUs with the conjugative transposon (Tc element). (A) RteB provided by the conjugative transposon activates expression of excisionintegration genes (, ) on the NBU. Products o f the excision gene(s), indicated here by Xis, act on the ends of the NBU to produce the excised circular form. (B) RteB, acting through R t eC (not shown), activates expression of genes on the conjugative transposon that are needed for mobilization of the NBU (indicated by Tra). The NBU produces a protein, Mob, that presumably nicks at the NBU and directs the single-stranded copy of the NBU to the mating pore provided by the conjugative transposon.

Citation: Salyers A, Shoemaker N, Stevens A. 1995. Tetracycline Regulation of Conjugal Transfer Genes, p 393-400. In Hoch J, Silhavy T (ed), Two-Component Signal Transduction. ASM Press, Washington, DC. doi: 10.1128/9781555818319.ch25
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Image of FIGURE 3
FIGURE 3

Model for tetracycline induction of transfer gene expression. and encode a two-component system, in which is the putative sensor and the putative response regulator. Tetracycline is actually sensed not through RteA but through the promoter of , the first gene in the operon that contains and . RteB activates expression of excision genes on the NBU and of . RteC counters the effect of a repressor, which normally represses synthesis of genes needed for transfer (indicated as ), and interacts with RteB to suppress its own synthesis. The repressor gene has not yet been located but lies outside the transfer and regulatory areas shown in Fig. 1 .

Citation: Salyers A, Shoemaker N, Stevens A. 1995. Tetracycline Regulation of Conjugal Transfer Genes, p 393-400. In Hoch J, Silhavy T (ed), Two-Component Signal Transduction. ASM Press, Washington, DC. doi: 10.1128/9781555818319.ch25
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Image of FIGURE 4
FIGURE 4

Modular structure of RteA and RteB. The output domains of RteA and RteB are shaded differendy to indicate that they differ in amino acid sequence. H and D indicate histidine and aspartate residues, respectively, which are involved in phosphorylation reactions. Redrawn from Parkinson and Kofoid (1992).

Citation: Salyers A, Shoemaker N, Stevens A. 1995. Tetracycline Regulation of Conjugal Transfer Genes, p 393-400. In Hoch J, Silhavy T (ed), Two-Component Signal Transduction. ASM Press, Washington, DC. doi: 10.1128/9781555818319.ch25
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References

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1. Arthur, M.,, C. Molinas,, and P. Courvalin. 1992. The VanS-VanR two component regulatory system controls synthesis of depsipeptide peptidoglycan precursors in Enterococcus faecium BM4147. J. Bacteriol. 174:25822591.
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3. Bonheyo, G. Unpubhshed data.
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9. Li, L. Y.,, N. B. Shoemaker,, and A. A. Salyers. Localization of the transfer origin (oriT) of a Bacteroides conjugative transposon and evidence for an additional layer of transfer genes. Submitted for publication.
10. Nikolich, M. Unpublished data.
11. Nikolich, M. P.,, N. B. Shoemaker,, and A. A. Salyers. 1992. A Bacteroides tetracycline resistance gene represents a new class of ribosome protection tetracycline resistance. Antimicrob. Agents Chemother. 36:10051012.
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14. Shoemaker, N. Unpublished data.
15. Shoemaker, N.,, and A. Stevens. Unpublished data.
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17. Shoemaker, N. B.,, and A. A. Salyers. 1990. A cryptic 65 kb transposon-like element isolated from Bacteroides uniformis has homology to the Bacteroides conjugal tetracycline resistance elements. J. Bacteriol. 172:16941702.
18. Shoemaker, N. B.,, G.-R. Wang,, A. M. Stevens,, and A. A. Salyers. 1993. Excision, transfer and integration of NBU1, a mobilizable site-selective insertion element. J. Bacteriol. 175:65786587.
19. Smith, C. J.,, and A. C. Parker. 1993. Identification of a circular intermediate in the transfer and transposition of Tn4555, a mobilizable transposon from Bacteroides species. J. Bacteriol. 175:26822691.
20. Speer, B. S.,, N. B. Shoemaker,, and A. A. Salyers. 1992. Resistance to tetracycline: mechanisms and transmission. Clin. Microbiol. Rev. 5:387399.
21. Stevens, A. M.,, J. M. Sanders,, N. B. Shoemaker,, and A. A. Salyers. 1992. Genes involved in production of plasmidlike forms by a Bacteroides conjugal chromosomal element share significant amino acid homology with two component regulatory systems. J. Bacteriol. 174:29352942.
22. Stevens, A. M.,, N. B. Shoemaker,, L.-Y. Li,, and A. A. Salyers. 1993. Tetracycline regulation of genes on Bacteroides conjugative transposons. J. Bacteriol. 175:61346141.
23. Stevens, A. M.,, N. B. Shoemaker,, and A. A. Salyers. 1990. Genes on a Bacteroides conjugal tetracycline resistance element which mediate production of plasmid-like forms from unlinked chromosomal DNA may be involved in transfer of the resistance element. J. Bacteriol. 172:42714279.
24. Valentine, P. J.,, N. B. Shoemaker,, and A. A. Salyers. 1988. Mobilization of Bacteroides plasmids by Bacteroides conjugal elements. J. Bacteriol. 170:13191324.

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