A recurrent translocation t(6;7)(q23;q34) in T-ALL involves the TCRB and C-MYB loci. (A) Partial R-banded karyotype with translocation t(6;7)(q23;q34). (B, left panel) FISH whole chromosome painting of chromosomes 6 (green) and 7 (red) on metaphases from leukemic cells confirmed the reciprocal translocation t(6;7). (B, right panel) Dual-color FISH analysis of the TCRB locus using TCRB-flanking probes (centromeric, CTD-3092H9 labeled in red; telomeric, RP11–168I15, labeled in green). Dissociation of the probes in leukemic cells with t(6;7) demonstrated the involvement of the TCRB locus as partner of the translocation. (C) Derivative sequences of t(6;7)(q23;q34) breakpoints in case TL34 and corresponding germ-line sequences. Recognition sequence signal (RSS) heptamer and putative heptamer-like sequence are indicated according to consensus⁵³ ; untemplated nucleotides (N-diversity) are typed in lowercase. GL indicates germ line; der, derivative chromosomes. Breakpoint sequences for cases T142 and UPN5846 are shown in Figure S1. (D) Southern blot mapping of the translocation breakpoint in case TL92 using a 6q23.3 probe derived from BAC RP11–388E23. Germ-line (GL) and TL34 (TCRB-MYB) DNAs are shown as negative and positive controls, respectively. EcoRI rearranged bands are shown by arrows. (E) Interphasic FISH screening of T-ALL using flanking C-MYB locus probes RP11–845K5 (green) and RP11–184J4 (red) identified additional MYB-translocated cases TL33 and TL93, further shown to juxtapose the TCRB and C-MYB loci using combinations of FISH probes. (F) Schematic representation of the der(6) genomic region of t(6;7), according to data from the IMGT database and the UCSC Genome Bioinformatics site, and to the DNA derivative sequence of the breakpoint region in case T142. An arrow indicates the breakpoint (BP). See “Patients, materials, and methods; Cytogenetic and molecular analyses” for details about FISH image acquisition and manipulation.