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Reference : UMR9198-FRABAR-005
Workplace : GIF SUR YVETTE,GIF SUR YVETTE
Date of publication : Friday, October 16, 2020
Type of Contract : FTC Scientist
Contract Period : 36 months
Expected date of employment : 1 March 2021
Proportion of work : Full time
Remuneration : Between 2 728 and 3 145 € depending on experience
Desired level of education : PhD
Experience required : Indifferent
Bacterial chromosomes are generally circular. DNA circularity can result in the formation of chromosome dimers, which physically impede the segregation of genetic information at cell division. Bacteria have evolved a highly conserved chromosomally encoded recombination (Xer) machinery to resolve chromosome dimers by the addition of crossovers at a specific unique site of their circular chromosomes, dif 1. Numerous mobile elements exploit Xer to integrate into the dif site of one of their host chromosomes 1. Integrative Mobile Elements exploiting Xer (IMEX) are often associated to pathogenicity. A salient example is provided by the evolutionary history of the agent of the cholera, Vibrio cholerae. The diarrhoea that is responsible for the epidemic propagation and high death rate associated with cholera is encoded in the genome of an IMEX, the cholera toxin phage (CTX) 2–4. Interactions between CTX and several other IMEX participate in the constant and rapid emergence of new cholera epidemic strains 5,6. Foremost among those is the toxin-linked cryptic satellite phage, TLC, whose integration seems to be a prerequisite for CTX integration 7.
The Xer machinery consists of two tyrosine recombinases, XerC and XerD, which each bind arm of dif and each catalyse a specific pair of strand-exchanges during recombination. Chromosome dimer resolution is under the control of a large integral membrane cell division protein, FtsK, which the catalytic activity of XerD by a direct contact. Plasmids and IMEX have evolved different mechanisms to escape the FtsK control 1. In most cases, they rely on the default activity of XerC 1–3,5,8. We showed that it is not the case for TLC 6 and identified a XerD activation factor in the genome of TLC, XafT 9.
XafT is a small cytoplasmic protein with no sequence or structural similarities to FtsK. Recent work from the lab indicates that XafT is not only a potent activator of XerD but also permits to recombine dif with sites lacking a bona fide XerD binding arm. The aim of the postdoctoral work is to further our understanding of the mechanisms of action of XafT by a combined approach of molecular biology and genetics, biochemistry and single molecule analysis. A related task will be to study how the different IMEX of V. cholerae interact with each other and how their interactions contribute to the dissemination of the cholera toxin genes in the environment.
1. Midonet, C. & Barre, F.-X. Xer Site-Specific Recombination: Promoting Vertical and Horizontal Transmission of Genetic Information. Microbiol. Spectr. 2, (2014).
2. Val, M.-E. et al. The Single-Stranded Genome of Phage CTX Is the Form Used for Integration into the Genome of Vibrio cholerae. Mol. Cell 19, 559–566 (2005).
3. Das, B., Bischerour, J., Val, M.-E. & Barre, F.-X. Molecular keys of the tropism of integration of the cholera toxin phage. Proc. Natl. Acad. Sci. 107, 4377–4382 (2010).
4. Martínez, E., Paly, E. & Barre, F.-X. CTXφ Replication Depends on the Histone-Like HU Protein and the UvrD Helicase. PLoS Genet 11, e1005256 (2015).
5. Das, B., Bischerour, J. & Barre, F.-X. VGJɸ integration and excision mechanisms contribute to the genetic diversity of Vibrio cholerae epidemic strains. Proc. Natl. Acad. Sci. 108, 2516–2521 (2011).
6. Midonet, C., Das, B., Paly, E. & Barre, F.-X. XerD-mediated FtsK-independent integration of TLCϕ into the Vibrio cholerae genome. Proc. Natl. Acad. Sci. 111, 16848–53 (2014).
7. Hassan, F., Kamruzzaman, M., Mekalanos, J. J. & Faruque, S. M. Satellite phage TLCphi enables toxigenic conversion by CTX phage through dif site alteration. Nature 467, 982–5 (2010).
8. Bischerour, J., Spangenberg, C. & Barre, F.-X. Holliday junction affinity of the base excision repair factor Endo III contributes to cholera toxin phage integration. EMBO J. 31, 3757–3767 (2012).
9. Midonet, C., Miele, S., Paly, E., Guerois, R. & Barre, F.-X. The TLCΦ satellite phage harbors a Xer recombination activation factor. Proc. Natl. Acad. Sci. 116, 18391–18396 (2019).
- molecular biology
- molecular genetics
The ideal candidate should have a solid experience of biochemistry and a good knowledge of molecular genetics
The team is housed in the genome biology department of the Institute for Integrative Biology of the Cell (I2BC), which provides a very stimulating research environment. The institute is situated in Gif sur Yvette, a pleasant village in the southern outskirts of Paris
Constraints and risks
Vibrio cholerae is a class 2 pathogen.
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