Acts as a novel regulator of senescence. Involved in the formation of senescence-associated heterochromatin foci (SAHF), which represses expression of proliferation-promoting genes. Binds to proliferation-promoting genes. May be required for replication-independent chromatin assembly (By similarity). Component of a complex that includes at least ASF1A, CABIN1, HIRA, histone H3.3 and UBN1. Interacts with HIRA (via WD repeat domain); the interaction is direct. Interacts with ASF1A, CEBPA, TJP1, TJP2 and TJP3 (By similarity). Localized as a nuclear speckled-like pattern in proliferating primary fibroblasts. Colocalizes with HIRA, PML and SP100 in PML bodies of senescent cells. Colocalizes with CLDN1. Detected along the upper granular cell layer of epidermis. When overexpressed, accumulates in the nucleus in cells showing defective cytokinesis (By similarity). Colocalizes with TJP1. Expressed in bile canaliculi in liver, in bronchiolar epithelium in lung and in tubular structures of gland ducts inside the olfactory epithelium and tongue epithelium. Belongs to the ubinuclein family.