Protein serine/threonine kinase HIPK2 phosphorylates RUNX1 upon formation of the RUNX1:CBFB complex. Serine residues S249 and S273 and threonine residue S276 of RUNX1 are phosphorylated by HIPK2. HIPK2-mediated phosphorylation of RUNX1 is implicated as an important regulatory step in hematopoiesis and is disrupted by leukemogenic mutations in CBFB (Aikawa et al. 2006, Wee et al. 2008).