Required for the periodic repression of histone gene transcription during the cell cycle (By similarity). Cooperates with ASF1A to promote replication-independent chromatin assembly. Required for the formation of senescence-associated heterochromatin foci (SAHF) and efficient senescence-associated cell cycle exit. Interacts with CCNA1, HIRIP3 and NFU1/HIRIP5 (By similarity). Part of a complex which includes ASF1A, CABIN1, histone H3.3, histone H4 and UBN1 (By similarity). Interacts with histone H2B, histone H3-3B, PAX3 and PAX7 (PubMed:9731536). Primarily, though not exclusively, localized to the nucleus (By similarity). Localizes to PML bodies immediately prior to onset of senescence (By similarity). Localizes specifically to the male nucleus in fertilized eggs. This localization persists from the initiation of sperm nucleus decondensation to pronucleus formation. Expressed in cerebrum, cerebellum, heart, kidney, liver, lung and spleen. Throughout development the long isoform is more abundant. In embryos, ubiquitously expressed with high levels detected in cranial neural folds, subregions of pharyngeal arches 1 and 2, circumpharyngeal neural crest and limb buds. Sumoylated. Phosphorylated by CDK2/CCNA1 and CDK2/CCNE1 on Thr-554 in vitro (By similarity). Also phosphorylated on Thr-554 in vivo. Embryonic stem cells (ES cells) exhibit accelerated differentiation in the early stages which may be attributable to increased availability of soluble histones. Belongs to the WD repeat HIR1 family.