Molecular characterization of the fusions. (A) TheAPI2-MLT products obtained by RT-PCR from case 1 (lane 1) and case 2 (lane 2). Size markers (M) are shown on the left, the negative control (−) is shown on the right. (B) The Southern blot detecting the rearranged EcoRI fragments of case 1. The probes were derived from an 8-kb EcoRI clone from chromosome 18 spanning the breakpoint (see Fig 2A, center). Lane 1 shows hybridization with the probe derived proximally to the breakpoint, lane 2 shows hybridization with the probe derived distally to the breakpoint. The arrow shows the normal 8-kb EcoRI fragment, the arrowheads show the chimeric fragments of, respectively, 7 kb, derived from the der(18) and 10 kb, originating from the der(11).