The translocation (1;14)(p34;q11) in human t‐cell leukemia: Chromosome breakage 25 kilobase pairs downstream of the tal1 protooncogene

Nearly 30 percent of patients with T‐cell acute lymphoblastic leukemia (T‐ALL) exhibit a tumor‐specific rearrangement of the TAL1 gene (also called TCL5 or SCL ). These rearrangements are generated by either local DNA deletion or a (1;14)(p34;q11) chromosome translocation, and they typically result in structural alterations of the TAL1 transcription unit. In this report we present a molecular characterization of the t(1;14)(p34;q11) from a T‐ALL patient. As a consequence of the translocation, TAL1 is transposed from its normal position on chromosome 1 into the T‐cell receptor α/δ chain locus on chromosome 14. Unlike previous cases, the chromosome 1 breakpoint in this patient did not disrupt the continuity of the TAL1 transcription unit, but instead occurred approximately 25 kilobase pairs (kb) downstream of TAL1 . This observation suggests that malignant alteration of TAL1 can be mediated by long‐range cis ‐activating mechanisms that are triggered by DNA rearrangement at a distant site.