Catalytic activity:ATP + a protein = ADP + a phosphoprotein. ,cofactor:Magnesium. ,enzyme regulation:Activated by phosphorylation on Ser-51 and Ser-555. ,Function: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. Hyperphosphorylates RS domain-containing proteins such as SFRS1 and SFRS2 on serine residues during metaphase but at lower levels during interphase. Locks onto SFRS1 to form a stable complex and processively phosphorylates the RS domain. Appears to mediate HBV core protein phosphorylation which is a prerequisite for pregenomic RNA encapsidation into viral capsids. ,similarity:Belongs to the protein kinase superfamily. CMGC Ser/Thr protein kinase family. ,similarity:Contains 1 protein kinase domain. ,subunit:Present in a seven component complex , the toposome , which separates entangled circular chromatin DNA during chromosome segregation. The extended N-terminal domain of isoform 1 binds to the nuclear scaffold-associated protein SAFB suggesting this isoform may phosphorylate splicing factors in close vicinity to the nuclear matrix. ,tissue specificity:Isoform 2 is predominantly expressed in the testis but is also present at lower levels in heart , ovary , small intestine , liver , kidney , pancreas and skeletal muscle. Isoform 1 is only seen in the testis , at lower levels than isoform 2. ,
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