While BTK is predominantly cytoplasmic and IK is predominantly nuclear, high-resolution fluorescence microscopy demonstrated that native IK and BTK are partially co-localized in the nucleus as well as cytoplasm of human B-lineage lymphoid cell lines ALL-N1 (Figure 1A), RAJI and DAUDI (Figure S3A in File S1). The gene discussed is BTK; the disease is acute lymphoblastic leukemia.