The homeodomain-interacting protein kinase (HIPK) family includes three members, HIPK1, HIPK2, and HIPK3. Each family member contains a conserved protein kinase domain as well as a separate domain, which interacts with homeoproteins. HIPK2 appears to act as a corepressor of homeodomain transcription factors, such as NK-3. Also, HIPK2 is regulated by ubiquitin-like modification via the covalent binding of SUMO-1. Subsequently, it is directed to nuclear bodies in vitro.