Localization of the MZL-1 translocation breakpoint in exon 1B of PAX-5. DNA from mononuclear cells of patients MZL-1 and PLL-1 was digested with HindIII or EcoRI followed by Southern blot analysis with the indicated DNA probes. The sizes of the hybridizing DNA fragments are indicated in kb to the left. The DNA fragments containing the reciprocal translocation breakpoints are highlighted in black. X denotes an unrelated DNA fragment that cross-hybridizes with the GC-rich DNA probe #2. A restriction map of the 5′ region of the PAX-5 locus8 is shown below together with the origin of the DNA probes and the hybridizingHindIII and EcoRI DNA fragments (sizes given in kb). Abbreviations: H, HindIII; E, EcoRI; S, SacI; BS, BstEII; P,PstI.