Flippase activator that phosphorylates DFN1 and DFN2 and which is involved in the generation of phospholipid asymmetry in membranes by the inward translocation of phospholipids. ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Belongs to the protein kinase superfamily. Ser/Thr protein kinase family. KIN82 subfamily.