To directly interrogate the relationship between RUNX1 and the fusion, we used the t(5;12) NALM-6 pre-B ALL cell line (Supplementary Table 2) which expresses wild-type RUNX1, generating a derivative expressing V5-tagged ETV6-RUNX1, facilitating independent immunoprecipitation of RUNX1 and the fusion. Here, ETV6 is linked to acute lymphoblastic leukemia.