In vivo Assembly of Bacterial Partition Condensates on Supercoiled and
Linear DNA
Abstract
In bacteria, faithful DNA segregation of chromosomes and plasmids is
mainly mediated by ParABS systems. These systems, consisting of a ParA
ATPase, a DNA binding ParB CTPase, and centromere sites parS,
orchestrate the separation of newly replicated DNA copies and their
intracellular positioning. Accurate segregation relies on the assembly
of a high-molecular-weight complex, comprising a few hundreds of ParB
dimers nucleated from parS sites. This complex assembles in a
multi-step process and exhibits dynamic liquid-droplet properties.
Despite various proposed models, the complete mechanism for partition
complex assembly remains elusive. This study investigates the impact of
DNA supercoiling on ParB DNA binding profiles in vivo, using the
ParABS system of the plasmid F. We found that variations in DNA
supercoiling does not significantly affect any steps in the assembly of
the partition complex. Furthermore, physical modeling, leveraging
ChIP-seq data from linear plasmids F, suggests that ParB sliding is
restricted to approximately 2-Kbp from parS, highlighting the
necessity for additional mechanisms beyond ParB sliding over DNA for
concentrating ParB into condensates nucleated at parS. Lastly,
explicit simulations of a polymer coated with bound ParB suggest a
dominant role for ParB-ParB interactions in DNA compaction within ParB
condensates.