TAL1, TAL2 and LYL1: a family of basic helix-loop-helix proteins implicated in T cell acute leukaemia.

TAL1 gene rearrangement is the most common genetic defect associated with T cell acute lymphoblastic leukaemia (T-ALL). Tumour-specific rearrangements of TAL1 arise as a result of either chromosome translocation or local DNA recombination. TAL1 gene products possess the basic helix-loop-helix (bHLH) motif, a DNA-binding domain common to several known transcription factors. The bHLH domain of TAL1 is especially homologous to those encoded by TAL2 and LYL1, distinct genes that were also identified on the basis of chromosomal rearrangement in T-ALL. Thus, TAL1, TAL2 and LYL1 constitute a unique family of bHLH proteins, each of which is a potential mediator of T cell leukaemogenesis.