NUMACOILED Nucleation mechanism for the auto-assembly of a large nucleoprotein complex on supercoiled DNA

NUMACOILED is an interdisciplinary project to study the cell cycle step driving DNA segregation in bacteria. Bacterial genomes are faithfully inherited at cell division. This essential biological process is mainly driven by self-specific DNA segregation systems present on chromosomes and low-copy number plasmids, namely ParABS systems. This project focuses on the auto-assembly of the large nucleoprotein complex that nucleates at the centromere site, parS, to form droplet-like clusters. By applying physical modeling on our in vivo and in vitro data, we have recently proposed a new model, termed ‘Nucleation & caging’, to explain the formation of this dynamical organization. To get further insights on this auto-assembly mechanism, we now aim (i) at understanding how only the ParB dimer bound to parS becomes competent to recruit all other ParB, and (ii) at implementing DNA supercoiling in our modeling. The experimental part will mainly involve genetic, microscopy and ChIP-sequencing approaches, and the theoretical part will involve numerical simulations of ring polymer with supercoiling at the base pair resolution together with analytical calculations. The outcomes of this project are numerous and extend beyond the bacterial world as auto-assembly of droplet-like organelles is likely universally shared amongst all organisms.