The element at −13 is capable of repressing luciferase expression under the control of either the SCL pro1a or SV40 promoters in erythroid (K562) and lymphoid (HPB-ALL) cells, consistent with the idea that it may regulate SCL expression when it is expressed in the erythroid lineage, and contribute to its silencing in the lymphoid lineage. The gene discussed is TAL1; the disease is acute lymphoblastic leukemia.