RT-PCR and schematic representation of the results. (A) Genomic structure of BTL and ETV6. The position of the PAC clones covering BTL was determined by Southern hybridization using oligonucleotides derived from the exon sequences (•, positive by hybridization; ○, negative by hybridization). The genomic structure of ETV6 was taken from Baens et al.12 The different primers used for PCR are shown in italics above the respective genomic structures. Exons are represented by gray boxes. E, EcoRI; H, HindIII. (B) Detection of the BTL-ETV6 and ETV6-BTL transcripts in the 4 cases by RT-PCR. Only the results of the second-round PCR are shown. nc, negative control. (C) Schematic representation of the predicted fusion proteins. Sequences derived from ETV6 are drawn in italics. Arrowheads mark the bounderies between the ETV6 and BTL parts. HR, hydrophobic region of BTL; HLH, helix-loop-helix domain of ETV6; ETS, DNA binding domain of ETV6.