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Abstract:
In bacteria, ParABSsystems and structural maintenance of chromosome
(SMC) condensin-like complexes are important for chromosome segregation
and organization. The rod-shapedMyxococcus xanthuscells have a unique
chromosome arrangement in which a scaffold composed of the BacNOP
bactofilins and PadC positions the essential ParB center dot
parSsegregation complexes and the DNA segregation ATPase ParA in the
subpolar regions. We identify the Smc and ScpAB subunits of the SMC
complex inM. xanthusand demonstrate that SMC is conditionally essential,
with Delta smcor Delta scpABmutants being temperature sensitive.
Inactivation of SMC caused defects in chromosome segregation and
organization. Lack of the BacNOP/PadC scaffold also caused chromosome
segregation defects but this scaffold is not essential for viability.
Inactivation of SMC was synthetic lethal with lack of the BacNOP/PadC
scaffold. Lack of SMC interfered with formation of the BacNOP/PadC
scaffold while lack of this scaffold did not interfere with chromosome
association by SMC. Altogether, our data support that three systems
function together to enable chromosome segregation inM. xanthus.
ParABSconstitutes the basic and essential machinery. SMC and the
BacNOP/PadC scaffold have different yet redundant roles in chromosome
segregation with SMC supporting individualization of daughter
chromosomes and BacNOP/PadC making the ParABS system operate more
robustly.
