HIPK2 is involved in RUNX1/ PEBP2-β–dependent p300 phosphorylation. (A) FLAG-p300 was transfected with RUNX1 and PEBP2-β in the presence or absence of wild-type or kinase-negative FLAG-tagged HIPK2 or DYRK1A, as indicated. Immunoblotting was performed on transiently transfected HEK293 cell lysates using the indicated antibodies. (B) Schematic representation of FLAG-tagged HIPK2 and DYRK1A proteins with functional domains used in panel A. KINASE indicates kinase catalytic domain; PEST, domain rich in proline, glutamate, serine, and threonine; YH, domain rich in tyrosine and histidine; H, histidine repeat; KN, catalytically inactive mutant.