Untangling bacterial DNA topoisomerases functions.

Topoisomerases are the main enzymes capable of resolving the topological constraints imposed by DNA transactions such as transcription or replication. All bacteria possess topoisomerases of different types. Although bacteria with circular replicons should encounter similar DNA topology issues, the distribution of topoisomerases varies from one bacterium to another, suggesting polymorphic functioning.

Transcription-induced domains form the elementary constraining building blocks of bacterial chromosomes.

Transcription generates local topological and mechanical constraints on the DNA fiber, leading to the generation of supercoiled chromosome domains in bacteria. However, the global impact of transcription on chromosome organization remains elusive, as the scale of genes and operons in bacteria remains well below the resolution of chromosomal contact maps generated using Hi-C (~5-10 kb). Here we combined sub-kb Hi-C contact maps and chromosome engineering to visualize individual transcriptional units.

DNA supercoiling in bacteria: state of play and challenges from a viewpoint of physics based modeling.

DNA supercoiling is central to many fundamental processes of living organisms. Its average level along the chromosome and over time reflects the dynamic equilibrium of opposite activities of topoisomerases, which are required to relax mechanical stresses that are inevitably produced during DNA replication and gene transcription. Supercoiling affects all scales of the spatio-temporal organization of bacterial DNA, from the base pair to the large scale chromosome conformation.

Assessing in vivo the impact of gene context on transcription through DNA supercoiling.

Gene context can have significant impact on gene expression but is currently not integrated in quantitative models of gene regulation despite known biophysical principles and quantitative in vitro measurements. Conceptually, the simplest gene context consists of a single gene framed by two topological barriers, known as the twin transcriptional-loop model, which illustrates the interplay between transcription and DNA supercoiling. In vivo, DNA supercoiling is additionally modulated by topoisomerases, whose modus operandi remains to be quantified.

The SMC-like RecN protein is at the crossroads of several genotoxic stress responses in .

Introduction: DNA damage repair (DDR) is an essential process for living organisms and contributes to genome maintenance and evolution. DDR involves different pathways including Homologous recombination (HR), Nucleotide Excision Repair (NER) and Base excision repair (BER) for example. The activity of each pathway is revealed with particular drug inducing lesions, but the repair of most DNA lesions depends on concomitant or subsequent action of the multiple pathways.