Chromosomes readily unlink from one another and segregate to daughter cells during cell division highlighting a remarkable ability of cells to organize long DNA molecules. SMC complexes mediate chromosome folding by DNA loop extrusion. In most bacteria, SMC complexes start loop extrusion at the ParB/parS partition complex formed near the replication origin. Whether they are recruited by recognizing a specific DNA structure in the partition complex or a protein component is unknown. By replacing

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... 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 chromosomes when transplanted into another organism. Using chimeric proteins and chemical cross-linking, we find that ParB binds to the Smc subunit directly. We map a binding interface to the Smc joint and the ParB CTP-binding domain. Structure prediction indicates how the ParB clamp presents DNA to the Smc complex to initiate DNA loop extrusion.