Cooperates with ASF1A to promote replication-independent chromatin assembly. Required for the periodic repression of histone gene transcription during the cell cycle. Required for the formation of senescence-associated heterochromatin foci (SAHF) and efficient senescence-associated cell cycle exit. Interacts with histone H3-3B, PAX3 and PAX7 (By similarity). Interacts with histone H3.Y (PubMed:28334823). Interacts with CCNA1, HIRIP3, NFU1/HIRIP5 and histone H2B. Part of a complex which includes ASF1A, CABIN1, histone H3.3, histone H4 and UBN1 (PubMed:11238922, PubMed:14680630, PubMed:14718166, PubMed:15621527, PubMed:16980972, PubMed:19029251, PubMed:9710638). Primarily, though not exclusively, localized to the nucleus. Localizes to PML bodies immediately prior to onset of senescence. Expressed at high levels in kidney, pancreas and skeletal muscle and at lower levels in brain, heart, liver, lung, and placenta. Expressed during embryogenesis. Sumoylated. Phosphorylated by CDK2/CCNA1 and CDK2/CCNE1 on Thr-555 in vitro. Also phosphorylated on Thr-555 and Ser-687 in vivo. Belongs to the WD repeat HIR1 family.