Public Thesis defense - LIBST

Functional interaction between Tn4430 replicative transposition and DNA replication by Ophélie d’UDEKEM d’ACOZ

Pour l’obtention du grade de Docteur en sciences

Transposable elements are major components of the genome of all living organisms, from bacteria to humans. Their ability to move or copy themselves from one position to another promotes chromosome rearrangements, gene mutation and dissemination of a variety of determinants, most notably antibiotic resistance genes. Therefore, transposable elements are now regarded as one of the main driving forces in evolutionary adaptation. Such an evolutionary success necessarily results from mutual adaptations between the different classes of elements and their hosts. However, very little is known regarding the mechanisms whereby transposons choose their target and communicate with the host cellular machineries to convert transposition intermediates into products.

In this thesis, we addressed this issue by using Tn4430 from Bacillus thuringiensis as a paradigm for the replicative transposition mechanism of the widespread Tn3-family of bacterial transposons. Recently, a ‘Replication Hijacking’ model for replicative transposition was proposed and according to this model, Tn4430 targets DNA replication or repair intermediates as a direct mechanism to recruit the host replication machinery during transposition. To deepen our understanding of this mechanism, we studied the functional and physical interaction between Tn4430 transposition complex and the replication machinery by using a combination of genetic, cellular and bio-informatics approaches such as Illumina-based high-throughput sequencing and high-resolution microscopy.

We first demonstrate that the transposon targets arrested replication forks in the host chromosome, providing strong evidences of an interaction between transposition and replication machineries to directly recruit the host replication proteins during replicative transposition. We then investigate Tn4430’s preference for small multi-copy plasmids instead of the chromosome or large conjugative plasmids. We also show the influence of the spatial and genetic environment on both the target and donor molecules on target site selection and the efficiency of transposition. Finally, we developed a set of tools to study the physical interaction between the transposition complex and replication machineries in live cells.

Together, these results help us understand the particular patterns of target site selection that optimize the element-host relationship and facilitate successful integration in the target.

Jury members :

• Prof. Bernard Hallet (UCLouvain), promoteur
• Prof. Michel Ghislain (UCLouvain), président
• Prof. Jacques Mahillon (UCLouvain), secrétaire
• Dr. François-Xavier Barre (CNRS, France)
• Prof. Rodrigo Reyes-Lamothe (McGill, Canada)

Pay attention :

The public defense of Ophélie d’Udekem d’Acoz scheduled for Friday 08 July at 04:00 p.m. will also take place in the form of a video conference

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