Acts both as a chaperone in the cytosol and as a chromatin regulator in the nucleus. When cytosolic, acts as a molecular chaperone: component of the ribosome-associated complex (RAC), a complex involved in folding or maintaining nascent polypeptides in a folding-competent state. In the RAC complex, stimulates the ATPase activity of the ribosome-associated pool of Hsp70-type chaperones HSPA14 that bind to the nascent polypeptide chain. When nuclear, mediates the switching from polycomb-repressed genes to an active state: specifically recruited at histone H2A ubiquitinated at 'Lys-119' (H2AK119ub), and promotes the displacement of the polycomb PRC1 complex from chromatin, thereby facilitating transcription activation. Component of ribosome-associated complex (RAC), a heterodimer composed of Hsp70/DnaK-type chaperone HSPA14 and Hsp40/DnaJ-type chaperone DNAJC2 (By similarity). Interacts (via ZRF1-UBD region) with ID1 (By similarity). The ZRF1-UBD region specifically recognizes and binds H2AK119ub. The ZRF1-UBD region is also involved in protein-protein interactions with other proteins, suggesting that it may be masked by some regulator, thereby preventing its association with H2AK119ub. Phosphorylated in M (mitotic) phase.