Distribution of TCF3-PBX1 breakpoints. The breakpoint cluster regions of TCF3 and PBX1 are shown. Blue boxes indicate exons. Known TCF3-PBX1 breakpoints are indicated by black vertical lines in the upper panel of each gene. Reciprocal PBX1-TCF3 breakpoints are depicted in the lower panel of each gene. For TCF3, a cluster region within the breakpoint cluster region is shown on bp resolution above the gene. Here, numbers indicate the number of reported breaks at this position. TCF3-PBX1 breaks are noted above the DNA strand, PBX1-TCF3 breaks below. The breaks reported in this study are shown in green (N15) and red (N141). Published breakpoints are taken from Wiemels et al,⁹  Paulsson et al,²⁰  Fischer et al,¹⁵  and previously unpublished breakpoints (M.M., unpublished data, September 2001).