Pleiotropic regulator of mitotic progression, participating in the control of spindle dynamics and chromosome separation. Phosphorylates different histones, myelin basic protein, beta-casein, and BICD2. Phosphorylates histone H3 on serine and threonine residues and beta-casein on serine residues Important for G1/S transition and S phase progression. Phosphorylates NEK6 and NEK7 and stimulates their activity by releasing the autoinhibitory functions of Tyr-108 and Tyr-97 respectively (By similarity). ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Homodimer. Binds to Ran GTPase. Has a greater affinity for Ran-GDP over Ran-GTP. Interacts with NEK6, NEK7 and BICD2. Interacts with SSRP1 and SUPT16H, the 2 subunits of the FACT complex. Interacts with DYNLL1; phosphorylation at Ser-949 strongly reduces DYNLL1 binding (By similarity). Dimerizes through its coiled-coil domain. Autophosphorylated on serine and threonine residues. When complexed with FACT, exhibits markedly elevated phosphorylation on Thr-210. During mitosis, not phosphorylated on Thr-210 (By similarity). Belongs to the protein kinase superfamily. NEK Ser/Thr protein kinase family. NIMA subfamily.