Nek5 (NimA-related protein kinase 5) is a 708 amino acid protein that is related to NIMA, a protein that was originally discovered in Aspergillus nidulans and is necessary for entry into mitosis. One of several members of the Set/Thr protein kinase super family, Nek5 contains one protein kinase domain through which it catalyzes the ATP-dependent phosphorylation of target proteins. Like NIMA, Nek5 may be involved in mitotic regulation and cell cycle control.