Hierarchical microtubule organization by condensates of different PRC1 constructs

It has been established that microtubule associated proteins (MAPs) can hierarchically organize microtubules into various structures in vitro. Recent research has suggested that liquid-liquid phase separation of MAPs, both in the cell and in vitro, could serve as a mechanism that results in microtubule organization. Here, we study the protein regulator of cytokinesis 1 (PRC1) MAP, an anti-parallel crosslinker known to condense into liquid droplets without the need for additional crowders. Using different constructs of PRC1, we examine the ability of its different structural domains to contribute to the formation of droplets and microtubule tactoids. We use fluorescence light microscopy to characterize the differences in properties between droplets and tactoids formed by different constructs. We find that completely omitting the N-terminal coiled-coil domain from PRC1 completely inhibits its ability to form tactoids and droplets in our assays. Omitting most, but not all of the coiled-coil domain affects ability to make droplets and tactoids, but does not completely suppress it. Surprisingly, completely omitting the intrinsically disordered c-terminal tail does not inhibit droplet or tactoid formation.