Wetting and localization of chromatin condensates by surface-enriched proteins

We put forward a novel mechanism for the positioning of chromatin within the cell nucleus that does not rely on polymer adsorption to the nuclear lamina. Using a field-theoretic model of a chromatin condensate formed through polymer--protein co-condensation, we show that surface enrichment of chromatin-binding proteins can localize the condensate at the nuclear lamina even when chromatin itself is repelled from the surface. The competition between the tendency of the protein component to wet the surface and the conformational restrictions of the polymer near the impenetrable boundary produces a nonmonotonic chromatin density profile with a maximum at a finite distance from the lamina, consistent with live-cell experiments [Sci. Adv. \textbf{7}, eabf6251 (2021)]. We further demonstrate that a non-binding protein competing for surface association can regulate the position of the condensate, providing an alternative pathway by which compositional changes of the lamina can induce chromatin repositioning. A phase diagram of the surface-localization transition reveals how surface affinity, protein availability, and polymer--protein interaction strength control the switch between peripheral and central chromatin configurations. This wetting-based mechanism contrasts with direct polymer adsorption and provides a general framework for understanding how multicomponent condensates interact with responsive biological surfaces.