Artificial TCF3-PBX2 and TCF3-PBX3 fusions, with the same part of TCF3 (amino acids 1 to 477) which is fused to PBX1 in t(1;19)-acute leukemias, displayed focus forming properties in NIH 3T3 fibroblasts comparable to those of the TCF3-PBX1 chimera, whereas none of the wild-type PBX2 and PBX3 proteins resulted in transformation of NIH 3T3 cells [26]. The gene discussed is PBX1; the disease is acute leukemia.