A joint-ParB interface promotes Smc DNA recruitment.

Chromosomes readily unlink and segregate to daughter cells during cell division, highlighting a remarkable ability of cells to organize long DNA molecules. SMC complexes promote DNA organization by loop extrusion. In most bacteria, chromosome folding initiates at dedicated start sites marked by the ParB/ parS partition complexes. Whether SMC complexes recognize a specific DNA structure in the partition complex or a protein component is unclear. By replacing genes in Bacillus subtilis with orthologous sequences from Streptococcus pneumoniae , we show that the three subunits of the bacterial Smc complex together with the ParB protein form a functional module that can organize and segregate foreign chromosomes. Using chimeric proteins and chemical cross-linking, we find that ParB directly binds the Smc subunit. We map an interface to the Smc joint and the ParB CTP-binding domain. Structure prediction indicates how the ParB clamp presents DNA to the Smc complex, presumably to initiate DNA loop extrusion. [Display omitted] • The bacterial DNA-binding protein ParB interacts with the condensin-like Smc-ScpAB • Genetic mapping and structure predictions reveal an Smc joint-ParB binding interface • Mutating the binding interface hampers Smc recruitment but not other ParB functions • ParB and Smc-ScpAB form a transplantable unit for chromosome segregation in bacteria By transplanting Streptococcus genes into Bacillus subtilis , Bock et al. demonstrate that a four-gene module comprising genes encoding ParB and the condensin-like subunits Smc, ScpA, and ScpB can promote chromosome segregation in foreign bacteria. They elucidate a ParB-Smc protein-protein interface and show it is required for Smc recruitment by ParB. [ABSTRACT FROM AUTHOR]