APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014;
Denver, Colorado
Session A12: Invited Session: Phase Trasitions in Biology
8:00 AM–11:00 AM,
Monday, March 3, 2014
Room: 205
Sponsoring
Unit:
DBIO
Chair: Cliff Brangwynne, Princeton University
Abstract ID: BAPS.2014.MAR.A12.4
Abstract: A12.00004 : Organizing the bacterial chromosome for division
9:48 AM–10:24 AM
Preview Abstract
Abstract
Author:
Chase Broedersz
(Princeton University)
The chromosome is highly organized in space in many bacteria, although the
origin and function of this organization remain unclear. This organization
is further complicated by the necessity for chromosome replication and
segregation. Partitioning proteins of the ParABS system mediate chromosomal
and plasmid segregation in a variety of bacteria. This segregation machinery
includes a large ParB-DNA complex consisting of roughly 1000 ParB dimers,
which localizes around one or a few centromere-like \textit{parS} sites near the origin
of replication. Despite the apparent simplicity of this segregation
machinery as compared to eukaryotic segregations systems, puzzles remain: In
particular, what is the nature of interactions among DNA-bound ParB
proteins, and how do these determine the organizational and functional
properties of the ParB-DNA partitioning complex? A crucial aspect of this
question is whether ParB spreads along the DNA to form a filamentous
protein-DNA complex with a 1D character, or rather assembles to form a 3D
complex on the DNA. Furthermore, it remains unclear how the presence of only
one or even a few \textit{parS} sites can lead to robust formation and localization of
such a large protein-DNA complex.
We developed a simple model for interacting proteins on DNA, and found that
a combination of 1D spreading bonds and a 3D bridging bond between ParB
proteins constitutes the minimal model for condensation of a 3D ParB-DNA
complex. These combined interactions provide an effective surface tension
that prevents fragmentation of the ParB-DNA complex. Thus, ParB spreads to
form multiple 1D domains on the DNA, connected in 3D by bridging
interactions to assemble into a 3D ParB-DNA condensate. Importantly, this
model accounts for recent experiments on ParB-induced gene-silencing and the
effect of a DNA ``roadblock'' on ParB localization. Furthermore, our model
provides a simple mechanism to explain how a single \textit{parS} site is both necessary
and sufficient for the formation and localization of the ParB-DNA complex.
To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2014.MAR.A12.4