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Abstract

In many bacteria, chromosome segregation requires the association of
ParB to the parS-containing centromeric region to form the partition
complex. However, the structure and formation of this complex have been
unclear. Recently, studies have revealed that CTP binding enables ParB
dimers to slide along DNA and condense the centromeric region through
the formation of DNA bridges. Using semi-flexible polymer simulations,
we demonstrate that these properties can explain partition complex
formation. Transient ParB bridges organize DNA into globular states or
hairpins and helical structures, depending on bridge lifetime, while
separate simulations show that ParB sliding reproduces the multi-peaked
binding profile observed in Caulobacter crescentus. Combining sliding
and bridging into a unified model, we find that short-lived ParB bridges
do not impede sliding and can reproduce both the binding profile and
condensation of the nucleoprotein complex. Overall, our model elucidates
the mechanism of partition complex formation and predicts its fine
structure.