SRPK is a family of key enzymes that regulate splicing activity in cells. The first serine-arginine (SR) protein kinase to be identified is SRPK1, which is isolated from mitotic cells and is described as phosphorylating SR proteins and promoting their release from the nuclear spot during the G2/M phase of the cell cycle. SRPK1 is the prototype of the SRPK family, which also includes two homologous SRPK2 and SRPK3 proteins. SRPK is characterized by dichotomous catalytic domains separated by unique spacer sequences and located primarily in the cytoplasm of mammalian cells. SRPK can be transferred to the nucleus under several conditions, such as during the G2/M phase of the cell cycle, or after osmotic stress, or as a result of activation of epidermal growth factor (EGF) signal transduction pathways.
