Dynamic ParB-DNA interactions initiate and maintain a partition condensate for bacterial chromosome segregation

Abstract

AbstractIn most bacteria, chromosome segregation is driven by the ParABSsystem where the CTPase protein ParB loads at theparSsite to trigger the formation of a large partition complex. Here, we presentin vitrostudies of the partition complex forBacillus subtilisParB, using single-molecule fluorescence microscopy and AFM imaging to show that transient ParB-ParB bridges are essential for forming DNA condensates. Molecular Dynamics simulations confirm that condensation occurs abruptly at a critical concentration of ParB and show that multimerization is a prerequisite for forming the partition complex. Magnetic tweezer force spectroscopy on mutant ParB proteins demonstrates that CTP hydrolysis at the N-terminal domain is essential for DNA condensation. Finally, we show that transcribing RNA polymerases can steadily traverse the ParB-DNA partition complex. These findings uncover how ParB forms a stable yet dynamic partition complex for chromosome segregation that induces DNA condensation and segregation while enabling replication and transcription.