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Abstract

Liquid-liquid phase separation is a fundamental biophysical process to organize eukaryotic and prokaryotic cytosols. While many biomolecular condensates are formed in the vicinity of, or even on lipid membranes, little is known about the interaction of protein condensates and lipid bilayers. In this study, we characterize the recently unknown phase behavior of the bacterial nucleoid occlusion protein Noc. We find that, similarly to other ParB-like proteins, CTP binding tightly regulates Noc's propensity to phase separate. As CTP-binding and hydrolysis also allows Noc to bind and spread on membranes, we furthermore establish Noc condensates as model system to investigate how lipid membranes can influence protein condensation and vice versa. Last, we show that Noc condensates can recruit FtsZ to the membrane, while this does not happen in the non-phase separated state. These findings suggest a new model of Noc mediated nucleoid occlusion, with membrane-mediated liquid-liquid phase separation as underlying principle of complex formation and regulation thereof.