 The Myst family protein HBO1 Myst2, KAT7 is a histone acetyl transferase that plays a major role in replication initiation and also contributes to DNA re-replication. HBO1 directly interacts with Cdt1 and functions as a coactivator of Cdt1 in replication initiation. It also associates with replication origin and stimulates origin activation by acetylating H4 K5, K8, and K12. Overexpression of HBO1 induces DNA re-replication. 