Identification and characterization of t(14;16)(q32;q23) translocation breakpoints. (A) Diagram of der(14) and der(16) breakpoints from translocations involving Sμ and Sγ. The centromere is to the left. Structural elements include enhancers (3′E and 5′E), switch region (S), and coding segments (rectangles). Thick horizontal lines depict hybridization probes. Vertical lines represent restriction enzyme sites. H, HindIII; Ba, BamHI; Bg,Bgl II. (B) Southern blots of MM cell line genomic DNAs digested with HindIII. Probes flanking switch regions are indicated at the bottom of each lane. For the ANBL6 line, 17-kb and 16.5-kb rearranged fragments are detected with the 5′ and 3′Sμ probes, respectively. For the MM.1 line, 4.9-kb and 7.7-kb rearranged fragments are detected with the 5′Sμ and 3′Sγ probes, respectively. The MM.1 4.0-kb fragment(s) that cohybridizes with 5′Sγ and 3′Sγ probes represents an unrearranged, germline fragment containing a γ switch region. (C) Map of region at 16q23 that contains c-maf and sequences present in the cloned t(14;16) breakpoint fragments. For the BAC clones (designated by number within box), the T7 (T) and SP6 (S) ends are shown when the orientation has been defined. Mapping was performed by using PCR reactions to detect sequences derived from the ends of BAC/P1 clones, translocation breakpoint fragments, and c-maf, plus 5 other chromosome 16 markers²⁸. The composite map is not to scale but is fully consistent with analysis of additional clones and markers that are not shown. The dashed arrow indicates that the t(16;22) breakpoint in 8226 is telomeric to c-maf by FISH analysis.