ASF1 Anti-Silencing Function 1 Homolog B （ASF1B） belongs to the H3/H4 family of histone chaperone proteins and is similar to the anti-silencing function-1 protein in yeast. ASF1B is the substrate of the tousled-like kinase family of cell cycle-regulated kinases， and may have a crucial role in modulating the nucleosome structure of chromatin by guaranteeing a regular supply of histones at sites of nucleosome assembly. ASF1B cooperates with CAF-1 （chromatin assembly factor 1） to stimulate replication-dependent chromatin assembly. ASF1B is highly expressed in the testis and at lower levels in colon， small intestine and thymus. ASF1B is necessary for spermatogenesis.
