TAL1 and acute lymphoblastic leukemia: However, the T allele reporter showed no increased activity over that of the C allele in human HEK-293 T cells (Figure 3f), suggesting that MYB and other members of the TAL1 complex expressed by Jurkat cells are required for the activation of gene expression from this site.5, 12 Taken together, we have shown that the somatically acquired C-to-T mutation that creates a MYB binding motif ~4 kb upstream of the proximal transcription start site of LMO1 in T-ALL can generate an active transcriptional enhancer that drives monoallelic overexpression of the LMO1 oncogene.