Summary of domain analysis of β/SMMHC. (A) Summary of earlier studies (top half) and this study (bottom half). Diagram shown at the top represents β/SMMHC. Red-colored segments—βE1 to βE5—represent exons encoding CBFβ/PEBP2β. ACD indicates assembly competence domain. (B) Diagrammatic models for RUNX1-β/SMMHC complex with varying SMMHC deletions. Center top shows the model proposed by Lukasik et al.³⁸  Lower drawings represent the models proposed by this study. NES indicates presumptive nuclear export signal; ACD, assembly competence domain; NHT, nonhelical terminus.