Serine-arginine protein kinases (SPRKs) constitute a relatively novel subfamily of serine-threonine kinases that specifically phosphorylate serine residues residing in serine-arginine⁄arginine-serine dipeptide motifs. Fifteen years of research subsequent to the purification and cloning of human SRPK1 as a SR splicing factor-phosphorylating protein have lead to the accumulation.