(A) SCL forms part of a multiprotein complex. SCL normally interacts with other transcription factors in erythroid cells to form a multiprotein complex that contains transcription factors such as GATA-1, LMO-2, LDB-1, and E2A proteins.74 As a result, “Gene A” is appropriately regulated. The precise stoichiometry of the complex is not known. (B and C) Models for the leukemogenic effect of SCL expression in T cells. (B) The leukemogenic effect of ectopic SCL expression in T cells may involve aberrant activation of target genes (Gene B), perhaps by a complex involving additional bHLH proteins (eg, X and Y).76 (C) Alternatively ectopic SCL expression may sequester E2A and/or other T-cell proteins (eg, Z), thereby upregulating or downregulating expression of their normal target genes (Gene C).