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DNA organization and segregation at super-resolution


Molecular Cell 
Volume 59, Issue 4, 20 August 2015, Pages 588–602

Condensin- and replication-mediated dynamic folding of a bacterial chromosome and its origin domain revealed by super-resolution imaging and Hi-C

Martial Marbouty*, Antoine Le Gall*, Diego I. Cattoni, Axel Cournac, Alan Koh, Jean-Bernard Fiche, Julien Mozziconacci, Heath Murray, Romain Koszul#, Marcelo Nollmann#

Chromosomes of a broad range of kingdoms, from bacteria to mammals, are structured by large topological domains, whose precise functional roles and regulatory mechanisms remain elusive. Here, we combine super-resolution microscopies and chromosome-capture technologies to unravel the higher-order organization of the Bacillus subtilis chromosome and its dynamic rearrangements during the cell cycle. We decipher the fine 3D architecture of the origin domain, revealing folding motifs regulated by condensin-like complexes. This organization, along with global folding throughout the genome, is present before replication, disrupted by active DNA replication and re-established thereafter. Single-cell analysis revealed a strict correspondence between sub-cellular localization of origin domains and their condensation state. Our results suggest that the precise 3D folding pattern of the origin domain plays a role in the regulation of replication initiation, chromosome organization and DNA segregation.

         Cell Systems, in press 
Stochastic Self-Assembly of ParB Proteins Builds the Bacterial DNA Segregation Apparatus

Aurore Sanchez,Diego I. Cattoni, Jean-Charles Walter, Jerome Rech, Andrea Parmeggiani, Marcelo Nollmann, and Jean-Yves Bouet

Many canonical processes in molecular biology rely on the dynamic assembly of higher-order nucleoprotein complexes. In bacteria, the assembly mechanism of ParABS , the nucleoprotein super-complex that actively segregates the bacterial chromosome and many plasmids, remains elusive. We combined super-resolution microscopy, quantitative genomewide surveys, biochemistry, and mathematical modeling to investigate the assembly of ParB at the centromere-like sequences parS . We found that nearly all ParB molecules are actively confined around parS by a network of synergistic protein-protein and protein-DNA interactions. Interrogation of the empirically determined, high-resolution ParB genomic distribution with modeling suggests that instead of binding only to specific sequences and subsequently spreading, ParB binds stochastically around parS over long distances. We propose a new model for the formation of the ParABS partition complex based on nucleation and caging: ParB forms a dynamic lattice with the DNA around parS . This assembly model and approach to characterizing large-scale, dynamic interactions between macromolecules may be generalizable to many unrelated machineries that self-assemble in superstructures

Chromosome organization: original condensins.

Cattoni DI, Le Gall A, Nöllmann M.

Curr Biol. 2014 Feb 3;24(3):R111-3. doi: 10.1016/j.cub.2013.12.033.