Schematic representation of the 14q32.3 (IGHlocus) and 4p16.3 regions. For the IGH locus, the relative location of the variable (V), diversity (D), joining (JH), and constant regions (μ, δ, γ, ɛ, ) is shown. For the 4p16.3 region, a scale representation is given. The location of breakpoints in MM cell lines (OPM2, JIM3, H929, UTMC2, KMS-11) and primary tumors (PCL-1, LB375, LB1017) is indicated by arrows; in case LB278, the breakpoint was localized by Southern blot (see Richelda et al13 and Chesi et al14 for more details). The relative position of the FGFR3 and WHSC1 genes (white box indicates the genomic region spanning the untranslated sequences) on the 4p16.3 region is illustrated (see Chesi et al,14 Thompson et al,17 Stec et al,18 Chesi et al,19and Baxendale et al24 for more details). Cosmid clones encompassing the WHSC1 locus24 are located. The portion of YAC 764-H1 encompassing the 4p16.3 region, as investigated by Southern blot and PCR analyses (see Materials and Methods), is shown by a solid line.