Functional interaction between Tn4430 replicative transposition and DNA replication

Transposons are mobile genetic elements that are able to move from one position to another within genomes. Little is known regarding the mechanisms whereby transposons choose their target and communicate with host cellular machineries to convert transposition intermediates into products. In this thesis, we addressed this issue by using the bacterial transposon Tn4430 belonging to the Tn3-family of replicative transposons. The recently proposed ‘Replication Hijacking’ model for replicative transposition suggests that 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. We first demonstrated that the transposon targets arrested replication forks in the host chromosome, providing strong evidences of an interaction between transposition and replication machineries. We then investigated Tn4430’s preference for small multi-copy plasmids instead of the chromosome or large conjugative plasmids. We also showed the influence of spatial and genetic environments on target site selection and on the efficiency of transposition. Finally, we developed a set of tools to study the physical interaction between the transposition complex and the replication machinery in living cells. Together, these results helped us understand the particular patterns of target site selection that optimize the element-host relationship and facilitate successful integration in the target.
(SC - Sciences) -- UCL, 2022