Binding of the RUNX1:CBFB complex to the promoter of the MYL9 gene stimulates MYL9 transcription. All four RUNX1 response elements in the MYL9 promoter contribute to transactivation of the MYL9 gene. The MYL9 gene encodes Myosin regulatory light polypeptide, which functions as a regulatory subunit of the myosin complex. Myosin plays an important role in platelet activation and thrombopoiesis. RUNX1 haploinsuficiency is associated with decreased MYL9 expression and myosin light chain phosphorylation, which likely contributes to thrombocytopenia and platelet dysfunction (Jalagadugula et al. 2010).