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Cohesins organize chromatin within the nucleus by promoting loop extrusion via cis contacts on chromatin and sister chromatid cohesion via trans contacts between chromatids. Whether cohesins employ a distinct mechanism for these two functions is not known. The authors use a carefully designed conditional expression of cohesin, mutated at its hinge domain, and assess its function with a variety of in vitro and in vivo experiments including live TIRF imaging, loop extrusion assay, Hi-C, and calibrated ChIP sequencing. A mutation in the hinge domain separates the two functions of cohesin, as the mutant supports loop extrusion but not sister chromatid cohesion. A unique mechanism of cohesins in promoting loop extrusion has implications for their distinct role in genome organization and for transcriptional regulation and cell fate determination. This study will be of broad interest to genome biologists with respect to these phenomena. This preprint has been assigned the following badges: New Hypothesis, New Materials. Read the preprint on bioRxiv ( Nagasaka et al., 2022 ): https://doi.org/10.1101/2022.09.23.509019 .