Regulatory subunit of the histone acetylase B (HAT-B) complex. The complex acetylates 'Lys-12' of histone H4 which is required for telomeric silencing (By similarity). Required for correct chromosome segregation where it has a role in the formation and/or maintenance of specialized chromatin at the centromere. Has a role in kinetochore assembly. Maintains the deacetylated state of histones specifically in the central core of the centromeres. {ECO:0000250|UniProtKB:P39984; ECO:0000269|PubMed:15369671}.