Serine/arginine-rich protein-specific kinase which specifically phosphorylates its substrates at serine residues located in regions rich in arginine/serine dipeptides, known as RS domains and is involved in the phosphorylation of SR splicing factors and the regulation of splicing. Plays a central role in the regulatory network for splicing, controlling the intranuclear distribution of splicing factors in interphase cells and the reorganization of nuclear speckles during mitosis. Can influence additional steps of mRNA maturation, as well as other cellular activities, such as chromatin reorganization in somatic and sperm cells and cell cycle progression. Phosphorylates SFRS2, ZRSR2, LBR and PRM1. Phosphorylates SRSF1 using a directional (C-terminal to N-terminal) and a dual-track mechanism incorporating both processive phosphorylation (in which the kinase stays attached to the substrate after each round of phosphorylation) and distributive phosphorylation steps (in which the kinase and substrate dissociate after each phosphorylation event). The RS domain of SRSF1 binds first to a docking groove in the large lobe of the kinase domain of SRPK1. This induces certain structural changes in SRPK1 and/or RRM2 domain of SRSF1, allowing RRM2 to bind the kinase and initiate phosphorylation. The cycles continue for several phosphorylation steps in a processive manner (steps 1-8) until the last few phosphorylation steps (approximately steps 9-12). During that time, a mechanical stress induces the unfolding of the beta-4 motif in RRM2, which then docks at the docking groove of SRPK1. This also signals RRM2 to begin to dissociate, which facilitates SRSF1 dissociation after phosphorylation is completed. Can mediate hepatitis B virus (HBV) core protein phosphorylation. It plays a negative role in the regulation of HBV replication through a mechanism not involving the phosphorylation of the core protein but by reducing the packaging efficiency of the pregenomic RNA (pgRNA) without affecting the formation of the viral core particles. Can induce splicing of exon 10 in MAPT/TAU (By similarity). ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Activated by phosphorylation on Ser-51 and Ser-548. Monomer. Found in a multisubunit complex containing seven proteins, named toposome, which separates entangled circular chromatin DNA during chromosome segregation. Interacts with HHV-1 ICP27 protein. Interacts with DNAJC8 and AHSA1/AHA1 and this mediates formation of a complex with the Hsp70 /Hsp90 machinery. Binds to IGF2BP1, SYNCRIP, HNRNPA2B1 and HNRNPC. Interacts with SAFB/SAFB1 and SAFB2 which inhibits its activity (By similarity). Shuttles between the nucleus and the cytoplasm (By similarity). Inhibition of the Hsp90 ATPase activity, osmotic stress and interaction with HHV-1 ICP27 protein can induce its translocation to the nucleus (By similarity). KAT5/TIP60 inhibits its nuclear translocation (By similarity). Preferentially localizes to the promoter of gene coding regions (By similarity). Predominantly expressed in the testis but is also present at lower levels in heart, spleen, liver, brain, kidney, lung and skeletal muscle. Present in all germinal cells in the seminiferous tubules but not in mature spermatozoa. Belongs to the protein kinase superfamily. CMGC Ser/Thr protein kinase family.