Southern blot analysis of IGH locus in MM samples. DNA was digested with the BamHI restriction enzyme and the nylon filters were subsequently hybridized to the probes indicated below. Germ-line bands are indicated in kilobases (kb) by dashes. The arrows indicate “illegitimate” IGH rearranged fragments that are candidates for chromosomal translocations and were cloned in cases LB375, LB1017, and LB411 (see text). (◃) Indicate comigrating JH and Cα rearranged fragments (“legitimate allele”) in MM cases expressing the IGH α isotype. (○) Indicate a 12-kb BamHI fragment cross-hybridizing with the JH probe in our experimental conditions. Germ-line JH and Cα BamHI fragments have approximately the same size in kb (*).