Thursday, 24th March, 2022

Valentin Quèbre will present their research on study of the DNA/Proteins complexes involved in bacterial DNA segregation.

Abstract :

Bacterial chromosomes and low copy number plasmids segregation is based on an active positioning mechanism. It consists in the partition systems that ensures the proper intracellular positioning of replicons to be faithfully transmitted to the daughter cells. The partition systems involves three cis-encoded partners. A DNA binding protein (ParB), is assembled in partition complexes at centromeric sequences (parS). An NTPase, which interacts with the partition complex, drives the segregation process and allows the complexes, and thus the plasmids, to be properly positioned inside the cell. My Ph.D project focused first on the better understanding of the partition complex assembly of the widespread type I system of the F plasmid and pESBL. Then, to decipher the global mechanism of the partition process of the recently discovered atypical system on R388, which does not involve any plasmid encoded NTPase to ensure its intracellular positioning.
Thus, my project is divided in three parts, aiming to (i) understand by an mutational approach, the initiation mechanism for the self-assembly of the majority of F plasmid ParB in a dynamic high molecular weight complex around parS, (ii) identify the pESBL partition system partners, in vitro characterize the ParB/parS interaction profile and in silico determine the group to which it belongs, (iii) identify the roles of the different domains of the R388 DNA binding protein StbA in its activities and characterize the StbA interaction modalities on its centromere by high throughput sequencing and biochemical approaches, to understand the partition complex architecture.
This study allows us to improve our knowledge on the Type I partition system and to shed light on the DNA/protein interaction specificities of an atypical system, carried by broad-host-range plasmids, opening the way to a better understanding of DNA segregation mechanism..

Gedy team- Jean-Yves Bouet and François Cornet