Structural Organization of the Mycobacterial Segrosome

Abstract

The structural organization of chromosomal partition assembly, which participates in chromosome partition in many bacteria, is poorly characterized. The partition protein ParB spreads on a large segment of DNA encompassing the centromeric parS site(s) to form the partition assembly, which is a higher order nucleoprotein complex of unknown nature. The partition assembly interacts with a number of proteins with diverse biological roles such as ParA, SMC proteins and origin tethering factors. We characterized the cross-sectional size parameters and internal organization of the partition assembly using solution X-ray and neutron scattering with hydrogen/deuterium contrast variation. Our data is consistent with a “DNA outside, protein inside” mode of partition assembly organization, in which the DNA is wrapping the protein from outside. In addition, we showed that mycobacterial ParA forms apparently ring-shaped polymers in vitro by electron microscopy. Based on our data, a testable model of interaction between the ParA polymer and the ParB-DNA partition assembly is proposed.